NBS

404

Radiochemical Analysis:

Activation Analysis, Instrumentation,

Radiation Techniques, and

Radioisotope Techniques

July 1965 through June 1966

Edited by James R. DeVoe

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U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

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THE NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 provides measurement and technical information services

essential to the efficiency and effectiveness of the work of the Nation's scientists and engineers. The

Bureau serves also as a focal point in the Federal Government for assuring maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. To

accomplish this mission, the Bureau is organized into three institutes covering broad program areas of research and services: THE INSTITUTE FOR BASIC STANDARDS . . . provides the central basis within the United

States for a complete and consistent system of physical measurements, coordinates that system with the measurement systems of other nations, and furnishes essential services leading to accurate and uniform

physical measurements throughout the Nation's scientific community, industry, and commerce. This

Institute comprises a series of divisions, each serving a classical subject matter area: —Applied Mathematics—Electricity—Metrology—Mechanics —Heat—Atomic Physics—Physical

Chemistry—Radiation Physics—Laboratory Astrophysics2—Radio Standards Laboratory,2 which

includes Radio Standards Physics and Radio Standards Engineering—Office of Standard Refer- ence Data. THE INSTITUTE FOR MATERIALS RESEARCH . . . conducts materials research and provides

associated materials services including mainly reference materials and data on the properties of materials. Beyond its direct interest to the Nation's scientists and engineers, this Institute yields services which are essential to the advancement of technology in industry and commerce. This Institute is or- ganized primarily by technical fields: —Analytical Chemistry—Metallurgy—Reactor Radiations—Polymers—Inorganic Materials—Cryogenics2—Materials Evaluation Laboratory—Office of Standard Reference Materials.

THE INSTITUTE FOR APPLIED TECHNOLOGY . . . provides technical services to promote the use of available technology and to facilitate technological innovation in industry and government. The

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1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D. C,

20234.

2 Located at Boulder, Colorado, 80302.

3 Located at 5285 Port Royal Road, Springfield, Virginia, 22151.
UNITED STATES DEPARTMENT OF COMMERCE • John T. Connor, Secretary

NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

NBS TECHNICAL NOTE 404

ISSUED SEPTEMBER 30, 1966

Radiochemical Analysis:

Activation Analysis, Instrumentation,

Radiation Techniques, and

Radioisotope Techniques

July 1965 through June 1966

Edited by James R. DeVoe

Radiochemical Analysis Section

Analytical Chemistry Division

Institute for Materials Research

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C., 20402 - Price $1.25
FOREWORD

The Analytical Chemistry Division was established as a

separate division at the National Bureau of Standards on

September 1, 1963, and became part of the Institute for

Materials Research in the February 1, 1964, reorganization.

It consists at present of nine sections and about 100 technical personnel encompassing some 45 different analytical competences from activation analysis and atomic absorption to

vacuum fusion and X-ray spectroscopy. These competences,

and in turn the sections which they comprise, are charged

with research at the forefront of analysis as well as awareness of the practical sample, be it standard reference material

or service analysis. In addition it is their responsibility

to inform others of their efforts.

Formal publication in scientific periodicals is highly

important. In addition, however, it has been our experience

that informal, annual summaries of progress describing efforts

of the past year can be very valuable in disseminating information. At the National Bureau of Standards such publications

fit logically into the category of a Technical Note. In 1966

we plan to issue these summaries for all of our sections

The following is the third annual report on progress of the

Radiochemical Analysis and Activation Analysis Sections.

W. Wayne Meinke, Chief

Analytical Chemistry Division

Li
PREFACE

During the period for which this report is written, the

Radiochemical Analysis Section was divided into two sections:

The Radiochemical Analysis Section and the Activation Analysis

Section. At the present time this split has only superficial

implications in that the sections have the same section chief

and this third progress report encompasses the activities of

both sections. Next year a progress report will be written

for each section.

It is the intent of these sections to develop measurement

techniques for the qualitative, quantitative and structural

analysis of materials through the use of radioisotopes. Since

the Analytical Chemistry Division is interested specifically in

the characterization of very pure materials, and since radiochemical methods are particularly suitable, a large portion of

these sections' effort is directed towards the analysis of very

small concentrations of the elements.

A basic requirement for the development of such measurement techniques using radioisotopes is the thorough understanding of the chemical, nuclear, and physical principles which form

the foundation of a new analytical measurement technique.

However, it is essential that the developed methods be practical

in the sense that they can be used successfully on materials

in which science and industry have an interest. Therefore,

these developed techniques are applied to the analysis of NBS

Standard Reference Materials where considerable cross checking

of analytical techniques is required throughout the process of

certification. Some misunderstanding has existed as to whether

the Analytical Chemistry Division certifies a particular analytical method. Under no circumstances is this done. The

material is certified for composition and therefore, it should

be independent of the analytical technique that is used. These

sections are attempting to make detailed error analyses of the

methods used to assure as high an accuracy as possible.

iii
The Activation Analysis Section is composed of the nuclear

reactor and the Linac group while the Radiochemical Analysis

Section retains the radiation techniques and radioisotope techniques groups. In addition, the Radiochemical Analysis Section

retains groups in nuclear instrumentation and nuclear chemistry

which consult with both sections.

A roster of the groups in these sections is listed in

part 7. The National Bureau of Standards has several programs

whereby a scientist from the United States or abroad may work

in our laboratories for one or two years. It is hoped that by

utilizing these programs the two sections will be able to perpetuate a stimulating environment.

In order to specify adequately the procedures, it has been

necessary occasionally to identify commercial materials and

equipment in this report. In no case does such identification

imply recommendation or endorsement by the National Bureau of

Standards , nor does it imply that the material or equipment

identified is necessarily the best available for the purpose.

James R. DeVoe , Chief

Radiochemical Analysis Section

and Activation Analysis Section

Analytical Chemistry Division

IV
TABLE OF CONTENTS

Page

1. INTRODUCTION 1

A. Liaison Activities 1

1. Scope of Liaison 1

2. Present Liaison with Other Government Agencies 2

B. Scope of Facilities 2

2

.

ACTIVATION ANALYSIS 5

A. Facilities 5

1. Nuclear Reactor 5

2

.

Fast Neutron Activation Facility 7

3

.

The NBS Linac 13

4. Naval Research Laboratory (NRL) Nuclear

Reactor 14

5

.

Digital Computer Facilities 18

B. Analyses with Nuclear Reactor 19

1. Determination of Copper in Standard Reference

Material 82b Nickel -Chromium Cast Iron by

Gamma-Gamma Sum Coincidence Spectrometry .... 19

2. Homogeneity Testing by Neutron Activation

Analysis: Determination of Homogeneity of

of Dissolved Metal Chelates in Military

Metal-in-Lubricating Oil Standards 2y

3. Fast Neutron Activation Analysis 36

4. Production and Use of Copper Foil Flux Monitors for High Precision Neutron Activation

Analysis Utilizing Short -Lived Radioisotopes 39

5. Resonance Neutron Activation Analysis ...... 47

6. Special Analyses 51

a. Selenium in Standard Reference Material

1170 Selenium Steel 51

b. Aluminum in SRM 14e Basic 52

c. Vanadium in SRM 73c Stainless Steel .... 53

d. Survey of Pure Titanium Metal 55

e. Determination of Impurities in Pyrolytic

Graphite 56

C. Photon Activation Analysis Using the NBS Linac 60

D. Experimental Design in Activation Analysis .... 62

v
Table of Contents (Cont.)

Page

E. Radiochemical Separations . .

71

F. Consultation and Liaison Activities 83

G. Publications . 83

3

INSTRUMENTATION * • • • • 84

A. Interface Unit s . . .

84

B. Time of Year (TOY) System 90

C. Time Mode Control Unit 92

D. Data Logging System 95

EFast Rise Preamplifier 95

F. Solid-State Detector Systems 97

G. Observations on Calibration of a Pulse Height

Analyzer Using a Sodium Iodide Detector ...... 97

H. Pneumatic Transport System Rabbit Sensor ..... 98

I. Consultation 100

4. RADIATION TECHNIQUES

Mftssbauer Spectroscopy 102

A. IntroductL on 102

B. Facilities 102

C. Computer Program for Curve Fitting of Mbssbauer

Spectra 108

D. Instrumentation 116

E

Search for Sn Standard 132

F. Consultations 135

G. Publications 136

5

RADIOISOTOPE TECHNIQUES 141

A. Facilities 141

B. The Application of Radioactive Isotopes to the

Quantitative Analysis of Trace Amounts of

Inorganic Substances on Paper and Thin Layer

Chromatograms 142

C. Differential Controlled-Potential Coulometry

Utilizing Radioisotopic Tracers 161

D. Radioisotopic Dilution for Trace Chemical

Analysis 170

vi
Table of Contents (Cont.)

Page

E. Publications • . « • . 178

F. Consultations ......... ....... ........... ...... 178

. J-i-LoX UJl1 1A1_iX\.d •••>..*. . . . . ............. ............. x. I j

1 . PERSONNEL 181

8 . ACKNOWLEDGMENTS 182

y . LXoi OF KJlir iLK.JtiJNL«iLbi ..•................•...••••••.•.. Xojt

APPENDIX I. NOTES ON THE USE OF THE G. E. TIME -SHARING

COMPUTER FOR MULT I COMPONENT DECAY CURVE ANALYSIS .. 187

APPENDIX II. FORTRAN PROGRAM FOR ANALYSIS OF MOSSBAUER

SPECTRA 208

vii
LIST OF FIGURES

Figure Page

1 Typical radiochemistry laboratory, B-Wing,

Buildingo 235 6

2 Neutron generator . . . . 8

3 Outside view of biological shield and console 9

4 Inside view of biological shield showing neutron generator in position 10

5 Floor plan of biological shield 11

6 Schematic design of pneumatic transfer system 12

Radiochemical hood and counting equipment in

the NRL radiochemistry laboratory 16

8 Pneumatic tube terminal and detector shield in

the NRL radiochemistry laboratory 17

9 Gamma-gamma sum coincidence spectrometer 22

10 Sample positioning with respect to the detectors 24

11 Normal gamma ray spectrum of SRM Cast Iron 82b 26

12 Sum coincidence spectrum of SRM Cast Iron 82b 27

13 Plot of averaged data from first (a) and second

(b) samplings with 95% confidence limits 34

14a Exploded view of copper foil flux monitor

mounted on cardboard base . . 43

14b Exploded view of a copper foil flux monitor

attachment to a sample container 43

15 Schematic of neutron spectrometer 50

16 Impurity radioactivity in pyrolytic graphite,

o child j. g j_#qcoo<-ooo ->••«••••••••••••*»••••• •••••• -" ^

17 Impurity radioactivity in pyrolytic graphite,

Sample 2 , second irradiation 59

18 Effect of mineral acids upon isotopic exchange

of cupric ion with 1% copper amalgam 78

vm
List of figures (cont.)

Figure Page

19 Plot of reaction rate versus reciprocal absolute

temperature ; 81

20 Interface translator (phase I) 85

21 Punch tape readin (phase II) 86

22 Precursor data (phase III) 87

23 System control circuit 89

24 Time of year clock 91

25 Time of year clock controller 93

26 Time mode control unit 94

27 Data logging system (block diagram) 95

28 Fast rise preamplifier for current signal 96

29 Calibration methods used with sodium iodide

detectors 98

30 Pneumatic tube system sensor 100

31 Certificate of calibration for MBssbauer standard, issued April 6, 1966 103-4

32 Radiochemical fume hoods and glass vacuum line 105

33 Control Console for constant acceleration spectrometer 106

34 Helium cryostat 107

35 Flow diagram of computer program for curve fitting of Mossbauer spectra 112

36 Loading instructions for computer program 113

37 Curve of fitted spectrum of standard crystal . 114

38 Curve of fitted spectrum of commercial iron foil 115

39 Cross sectional view of powder cell assembly .

.

116

40 Curve of fitted spectrum of Sn0

2

118

41 Phantom view of furnace 119

ix
List of figures (cont.)

Figure Page

42 Multiplex 123

43 Channel advance pulse gating circuit 125

44 Interlock circuit 127

45 Schematic of gas flow system . 129

46 Plot of the signal-to-noise ratio of the gas

flow detector compared to the sealed detector

for the 14.4 MeV gamma ray 130

47 Plot of the relative efficiency of the two

detectors 131

48 Graph of relative intensity of the ratio 14.4

keV gamma ray to the 6.3 keV X-ray versus

thickness of the aluminum filter 133

49 Pulse height spectrum of low energy region of

57Co through 9 mil of Al foil 134

50 Nuclear instrumentation room containing automatic proportion and gamma counting system .. 142

51 Radiochemical laboratory module for substoichiometric radioisotopic dilution analysis (SRDA) 143

52 Other half of SRDA laboratory 144

53 Radiometric laboratory 145

54 Radiometric laboratory 146

55 Separation of cations by paper and thin layer

chromatography 156

56 Schematic diagram for differential controlledpotential coulometry 163

57 Diagram of apparatus 164

58 Potential of sample cell vs time for various

concentration ratios 169
LIST OF TABLES

Table Page

1 Approximate composition of SRM 82b, nickel

chromium cast iron .................... 20

2 Results of activation analysis for copper in

3 Normalized percentages of aluminum and copper

in military metal-in-lubricating oil standards » — jCxrsc sampjLi.ng *>•.»«*«...«...•.....«>•.•««•.« o<£

4 Normalized percentages of aluminum and copper,

military metal-in-lubricating oil standards

" Second Scimp jl jlxi& «»*««»e»**9»*«**«**#««#*«0<» <»<»<» j? o

5 Comparison of aluminum and copper composite

samples with averages for same elements at 1,

50, and 500 ppm (data in normalized percent)..,. 36

6 Useful information on commonly used flux monitors 41

7 Flux monitor reproducibility ................... s 45

8 Resonance neutron activation, resonance integrals

and induced radioactivity ...................... 49

9 Impurity levels in pyrolytic graphite .......... 57

10 External absorption factor (f ) for aluminum ab11 Self-absorption factor (f ) 66

12 Detection limits 70

13 Separation of copper and contaminants by amalgam

exchange 77

14 Activation analysis results 79

15 Summary of kinetic data 80

16 Relationship between shim thickness and cell

thickness 117

17 Colorimetric reagent

s

153

18 Nickel oxide Standard Reference Material 671 . . . 159

XI
List of tables (cont.)

Table No. Page

19 Summary of the results of the determination

of Cadmium (II) in 0.1 M KN0

3

167

20 Results obtained with zinc 176

21 Determination of Mercury 176

Xll
RADIOCHEMICAL ANALYSIS: ACTIVATION ANALYSIS, INSTRUMENTATION,

RADIATION TECHNIQUES, AND RADIOISOTOPE TECHNIQUES

July 1965 to June 1966

Edited by James R. DeVoe

ABSTRACT

This is the third summary of progress of radiochemical

analysis which encompasses the work of both the Radiochemical

Analysis and Activation Analysis Sections of the Analytical

Chemistry Division at the National Bureau of Standards.

Pertinent information on the irradiation facilities of

the nuclear reactor, Linac , and Cockroft -Walton generator

are described. A number of analyses of standard reference

materials by activation analysis are described (e.g. , Cu in

cast iron, SRM 82b; Se in selenium steel, SRM 1170; Al in steel,

SRM 14e; and V in stainless steel, SRM 73c). Various aspects

of the technical problems in activation analysis such as its

use for homogeneity testing, production of suitable flux monitors, and experimental design with respect to increasing

selectivity (such as by using variable neutron energy) and

reducing systematic and random errors, are presented. A

realistic procedure for estimating sensitivity and for designing the analysis to optimize the detection limit is described.

A computer program that resolves complex decay curves utilizes

parameter changes convenient for the conversational aspect of

"time sharing" digital computers. A highly specific radiochemical separation for copper using a type of amalgam exchange

is described.

Description of specialized data handling equipment as well

as information on a fast rise preamplifier, solid state detector system, and other special instruments such as a pneumatic

transport system rabbit sensor, are presented.

A description of the laboratories used in M5ssbauer spectroscopy is presented. Special problems in radiation detection

xiii
for use in a spectrometer are also described. The Standard

Reference Material Program for chemical shift in MBssbauer

spectroscopy is discussed with particular reference to the

search for a tin standard. The computer program, n Parlors M, TT that is used for resolving complex Mossbauer spectra is presented in its entirety in Appendix II.

The use of thin layer chromatography in conjunction with

radioactive reagent analysis for trace elements is described.

Substoichiometric radioisotope dilution continues to be studied

by evaluating systematic and random errors, as well as by

developing the technique from physico-chemical principles such

as controlled potential coulometry.

James R. DeVoe, Chief

Radiochemical Analysis Section

and Activation Analysis Section

Analytical Chemistry Division

Key words

NBS reactor, NBS Linac , Cockroft -Walton generator, digital

computers, activation analysis, standard reference materials,

photo-neutron reactions, flux monitors, Cu, Se , Al, V in irons

and steels; homogeneity testing, pneumatic rabbit sensor,

MSssbauer spectroscopy, tin standard for chemical shift,

PARLORS program for Mossbauer spectra, Mossbauer instrumentation, M&ssbauer laboratories, radiometric trace> chromatography,

radioisotope dilution, subscoichiometry by controlled potential

coulometry, radiochemical separations, theoretical detection

limits for activation analysis, CLSQ program for multicomponent

decay, solid state detectors, electronic data handling.

xiv
1. INTRODUCTION

A. Liaison Activities

1. Scope of Liaison

It has been found to be extremely valuable to have one

person (called the Radiochemistry Coordinator) at the NBS

nuclear reactor facility who can coordinate the activities of

the radiochemists with the reactor personnel. The following

areas of coordination are encompassed in the liaison activity:

a. Inform and obtain approval from the reactor

utilization committee for all changes to existing radiochemical facilities in the reactor building. This includes

modification of hoods in the radiochemical laboratories,

installation of additional facilities such as the clean room,

Cockroft-Walton neutron generator, counting rooms, pneumatic

tube facilities and special cooling water installations, for

example. The project leaders ascertain the extent of facilities, modifications or installations and submit this information to the coordinator who in turn secures the necessary

approval.

b. Coordinate the use of existing facilities by

radiochemists with respect to reactor utilization (such as

requests for irradiations) , laboratory utilization, and

health physics. This activity performs the function of

informing the radiochemists about the proper procedure for

utilizing the reactor facilities and of working with the

reactor personnel on the formulation of proper operating

procedures.

c. Perform the functions stated in a and b above,

with all radiochemists using the facilities in the reactor

building. This includes radiochemists from other laboratories

as well as those from the National Bureau of Standards.
2. Present Liaison with Other Government Agencies

It is the expressed intent of the Director of the Nuclear

Reactor to make the wide range of facilities that have been

discussed in other reports [1, pp 9-12; 2; 3] available to

representatives other than those at the National Bureau of

Standards when such facilities are not already being used to

full capacity and when the proposed work fulfills a mission

of NBS.

An information meeting was held in July 1965 for the purpose of explaining the available irradiation facilities and

radiochemical laboratories in the reactor facility. This

meeting was attended by representatives of the Atomic Energy

Commission, Federal Bureau of Investigation, Food and Drug

Administration, Internal Revenue Service, Post Office Department, U. S. Coast Guard Oceanographic Unit, U. S. Geological

Survey and the University of Maryland.

The U. S. Geological Survey has negotiated an agreement to

use radiochemical laboratory space and the reactor irradiation

facility. Negotiations are in progress with the Internal

Revenue Service, Food and Drug Administration and the Post

Office Department.

It is of particular importance for the efficient operation

of the radiochemistry laboratory in the reactor building to

have the Radiochemistry Coordinator be the central focal point

for assisting these scientists from other laboratories.

B. Scope of Facilities

Since a variety of facilities is becoming available to both

the Activation Analysis and Radiochemical Analysis Sections, it

is expedient to describe these facilities in each of the research categories presented in this report. Considerable progress has been made in reaching an operable state in each of the

projects since we have occupied the reactor building and the

general purpose laboratories in Gaithersburg. The nuclear reactor being operated by Division 314 is expected to go critical
in the fall of 1966 with full power operation expected in

early 1967.

In spite of the difficulties resulting from the fact that

the reactor is not yet in operation, the work by the Activation

Analysis Section on certification of standard reference materials has been progressing very well. We are continuing to use

the Naval Research Laboratory's reactor, but since we are now

occupying our own laboratories in the NBS reactor many samples

are transported to our laboratories after irradiation.

The linear electron accelerator, being operated by Division

231, has become operational in a limited sense, and our group

was the first to assemble a target in the beam. We expect to

gain much information in the next few months on the potential

of the NBS machine for our research projects.

A 14-MeV neutron generator in the Activation Analysis

Section is close to operation and will be used initially to

support the Standard Reference Material Program in the area

of oxygen analysis.

The basic equipment for performing a variety of radiation

spectroscopies is now available as is the necessary equipment

(produced by the nuclear instrumentation group in the Radiochemical Analysis Section) for handling large amounts of data.

Studies are continuing on radiochemical separations , and

a careful investigation of the detection sensitivity, accuracy

and precision in activation analysis is being made.

The group in radiation techniques has completed work on

the standard reference material for chemical shift of iron

compounds in Mbssbauer spectroscopy. In conjunction with this

work was the modification of the NBS spectrometer to allow the

simultaneous analysis of two absorbers on the same electromechanical drive. This dual spectrum approach results in a

significant increase in precision of the spectral parameters.

Considerable advance has been made in the interpretation of

these parameters with respect to structural chemical determinations.

3
Efforts have been successfully made to improve upon the

sensitivity of the radioisotopic tracer techniques. The development of radiochromatographic separations of many elements

suggests that it is feasible to consider that complementary

radiometric methods present a satisfactory multi-element trace

analysis. The use of radioisotope dilution in electrochemical

separations indicates that better sensitivity may be obtained

than the usual methods which measure current.

Now that our move to Gaithersburg is completed, greater

effort will be placed on research in areas that will improve

measurement techniques and in areas that have not been carefully studied with respect to their application to analytical

chemistry.
2. ACTIVATION ANALYSIS

A. Facilities

1. Nuclear Reactor

Work has progressed toward completion of modifications of

laboratories and existing pneumatic tube facilities at the

NBS reactor. The completed laboratories in the cold and warm

areas are now being occupied by personnel from the Activation

Analysis and Radiochemical Analysis Sections. Future plans

will include completion of the radiological laboratories with

their counting room, the neutron generator facility, a clean

room, changes in hood exhaust systems and an extended pneumatic

tube system.

Seven laboratories have been remodeled in the warm (B-wing)

area by replacing fume-type hoods with stainless steel radioactivity hoods, which doubles the hood space available. Also

modified were the sink units, to give stainless steel sinks

and drainboards. A typical radiochemistry laboratory, used for

moderate levels (tens of mCi) of radioactivity, is shown in

figure 1. Other modifications made in this area include two

laboratories in which benches and cabinets were installed for

use as counting rooms.

Our higher level radiochemical separations and activation

analyses will be carried out in the radiological laboratories

in the C-wing area below the reactor in the Reactor Building.

Modifications [1] in this area are in progress and include an

island of four hoods in room C-001, with the pneumatic tube

receivers in a single eight-foot hood. In the adjoining radiological laboratory (C-002) the pneumatic tube receivers are

being recessed into each of four radiochemical hoods around the

periphery of the room in order to minimize contamination in

transfer for radiochemical separations. Samples will be transferred for counting by a pneumatic shuttle system to the adjoining counting room C-003.

A clean room is being constructed in the hot cell area (Bwing) to give a dust-free, controlled environment for activation

5
Figure 1. Typical radiochemistry laboratory

B-Wing, Building 235
analysis sample preparation. This room, constructed of modular

demountable steel panels, has working dimensions of approximately 15 by 22 feet, and an anteroom for change to particulatefree clothing. The room uses the horizontal laminar air-flow

principle, with all air filtered through "absolute" filters to

reduce impurity dust to a minimum. A hood, benches, and glove

boxes are located in the room for chemical and physical operations. It is anticipated that the use of this clean room will

assist in the attainment of a new dimension in the sensitivities

for activation analysis for trace constituents in many materials.

As discussed in the previous annual progress report [1, pp 2

and 3], we plan to extend the pneumatic tube system to include

five new terminals in the NBSR. These will include two in the

top of the core, one in the fast flux converter thimble, one in

the thermal column and one in a liquid nitrogen cooled terminal.

At least one receiver and sending device from the reactor terminals will be installed at a later date in a hood in each of the

modified B-wing laboratories.

(G. W. Smith)

2. Fast Neutron Activation Facility

This facility, located in the hot cell bay (room B125) in

building 235, essentially consists of a 14-MeV neutron generator

housed in a biological shield. It also includes provisions for

incorporation of pneumatic transfer systems, associated counting equipment and essential services.

a. Neutron Generator . The Activatron 210* (Technical

Measurement Corporation) neutron generator (figure 2) is capable of a maximum deuteron beam current of 500 /xk producing a

10 -1 maximum output of 2 x 10 n»s at the tritium target. The

9 -2 -1 maximum usable flux is of the order of 3 x 10 n.cm s Neutrons are produced by bombarding a tritium loaded target

3 .4

with 150 keV deuterons producing the H(d,n) He reaction. The

neutron output is essentially monoenergetic and isotropic.

* For disclaimer of equipment and materials see last paragraph

of preface.

7
/

Figure 2. Neutron Generator

8
The accelerator is assembled and operating. Preliminary

evaluation of the machine using a beam of hydrogen gas shows

it to be capable of its rated beam output. Over a period of

about two hours, the beam is found to be stable within ±57o at

peak beam intensity and ±37o at 50% beam intensity.

b. Biological Shield . The protective shield (figures

3 and 4) occupies an area approximating 450 square feet. It

consists of a 7 ft high and 32 in thick outer wall within which

is enclosed an inner shield which is approximately 6 ft 4 in

high and 24 in thick. The inner shield encloses a 2 ft x 4 ft

x 5 ft deep experimental well over which slides a 16 in thick

overlapping lid.

Figure 3. Outside view of biological shield and console

9
Figure 4. Inside view of biological shield showing

neutron generator in position

10
A

/

•-32-

SLIDING HIGH DENSITY CONCRETE

DOOR

LOW DENSITY CONCRETE

OUTER SHIELD

EXISTING STEEL

Figure 5. Floor plan of biological shield

The outer structure is constructed from 4 in x 8 in x 16 in

standard concrete blocks (~130 lb/ft ) stacked in an interlocking pattern. The bulk of the inner shield is identically

stacked using 8 in x 8 in x 12 in iron aggregate high density

blocks (^180 lb/ft ). Entry to the facility is made through

an interlocked safety door. Allowance has been made in the

inner shield for exit and entry of the pneumatic tubes. A view

of the plan for the biological shield is shown in figure 5.

Except for the high density blocks, the entire shield structure

is painted with water-sealing paint.

Except for the lid over the inner shield and the safety

door, the entire structure is essentially complete and ready

to house the neutron generator. Design and construction of

the lid and safety door are in progress.

11
c. Pneumatic Transfer System , The primary system

design includes a special dual-birotational sample target assembly. The system controller design allows for simultaneous

irradiation and sequential counting of the standard and unknown

between two 4 in x 3 in Nal(Tl) scintillation detectors connected to a 400-channel pulse height analyzer system. Other

significant details include irradiations in a nitrogen atmosphere, manual and semiautomatic operation modes, and a sample

spinning device. A general block diagram (figure 6) illustrates

the design layout of this system.

The rotating target assembly is essentially complete and

awaiting motor driving mechanisms. The controller is partially

designed. The operating sequence of the entire system has been

worked out and is ready to be incorporated in the controller

design.

Provisions have been made for the proper handling of

tritium targets in a glove box during installation and disposal.

The exhaust from the roughing pump will be vented via the glove

box exhaust.

SOLENOID VALVE

DRY NITROGEN PRESSURE GAUGE BLEED GAS CONTROL

ROTATING TARGET ASSEMBL

ROUTING VALVE RABBIT CONTROLLER VENT

SCINTILLATION DETECTOR

SOLENOID PIN AIR CONTROLLER

AIR FILTER COMPRESSED AIR RECEIVER SAMPLE

Figure 6. Schematic design of pneumatic transfer system

12
2 A compressed air line ( 70 lb/in ) and essential electrical

services have been provided.

(S. Nargolwalla and G. W. Smith)

3. The NBS Linac

A forty-kilowatt microwave linear electron accelerator has

been installed in building 245 at the NBS Gaithersburg facility.

By utilizing suitable radiators to intercept the electron beam,

large quantities of high energy bremsstrahlung can be generated.

These high energy photons can induce photonuclear reactions in

many elements , giving rise to radioactive products. We have

designed and constructed a bremsstrahlung target and associated

pneumatic transfer equipment and are currently testing it.

a. Target . The electrons from the accelerator enter

the target assembly through a three -inch diameter titanium

window of 0.003 inches in thickness. The photon producing targets consist of six tungsten discs, 2 inches in diameter and

0.008 inches in thickness. Since pure tungsten has a tendency

to flake, 100 microinches of gold has been plated on the discs

to prevent contaminating the cooling water.

The tungsten discs are held in position by stainless steel

plates which maintain a separation of 0.125 inches between the

target elements. This is for circulation of cooling water.

Three inches of water behind the last target plate absorb most

of the electron beam not converted in the tungsten.

Since the total mass of the target assembly is susceptible

to heating by scattered radiation, a stainless steel water

jacket surrounds it. Iron-constantan thermocouples monitor

the temperature of the target assembly as well as the rest of

the apparatus.

The flow rate of cooling water through the target can be

adjusted remotely by means of a motor driven assembly coupled

to gate valves in the inlet line.

b<. Pneumatic Transfer System . A pneumatic system

! with several receiving locations is being installed for transfer of the sample to and from the target area.

13
The terminal section at the target end is located directly

behind the target assembly. The sample, upon arriving at the

irradiation position strikes a microswitch actuating arm providing a positive signal of its arrival.

Air is injected into the terminal tube at a tangent to the

tube about one inch below the tube. This spins the rabbit,

cooling it and allowing a more homogeneous irradiation.

At the end of a preset irradiation, the spinning air is automatically turned off and return air turned on, bringing the

sample back to the desired receiving location.

c. Beam Absorbers . It is necessary to absorb the

intense photon and associated neutron flux produced in the

target to prevent activation and thermal damage to the environment of the assembly. The target and sample terminal are

surrounded by an annulus of high purity, water-cooled lead in

a stainless steel jacket. Three inches of lead surround the

target assembly and sample terminal on the side and nine inches

absorb the direct photon beam.

Details on the design of this system will be published at

a later date.

(F. A. Lundgren and G. J. Lutz)

4. Naval Research Laboratory (NRL) Nuclear Reactor

In anticipation of the extensive program in neutron activation analysis to be carried on at the NBS reactor when it

becomes operational, a small program was started in 1964 utilizing the facilities of the Naval Research Laboratory nuclear

reactor, located in southeast Washington, D. C. The primary

objective of this program was to gain experience in the experimental aspects of neutron activation analysis. A secondary

objective was to carry on as much of a program in research and

actual analysis as possible, the samples primarily originating

either with the NBS Standard Reference Material Program or as

service analyses.

14
The NRL Reactor is a 1-megawatt swimming pool type, with

a rectangular core grid currently using 30 grid positions.

Three in-core irradiation positions are available (Glory tubes

Nos. 1, 1A, and 2) at a thermal neutron flux of approximately

12 -2 -1

8 x 10 n»cm s and a gold-cadmium ratio of 2 to 3. In

addition, two pneumatic tube terminals are located on graphite

ledges above and to each side of the core. These pneumatic

12 tube terminals have a thermal neutron flux of about 0.8 x 10

-2 -1 ' n«cm s and a gold-cadmium ratio of 11.0. It has previously

been reported that these pneumatic tube irradiation positions

have a significant neutron flux gradient in both the vertical

and horizontal directions [1, p 41]. The Analytical Chemistry

Division of NBS leased a radiochemical hood and associated space

in the radiochemistry laboratory located in the NRL reactor

building. This has enabled the use of our own detector system

and multi-channel analyzer for the analysis of very short-lived

radioisotopes (e.g., 17.5 s Se , and 19 s Hf) and allowed

radiochemical separations when necessary with a minimum of

delay (figures 7 and 8). A pneumatic tube delivery terminal

located just outside the radiochemistry laboratory, with an

opening through the wall for rapid handling of irradiated

samples, has been indispensable in the analysis of short halflife radioisotopes (figure 8). The 3 in x 3 in Nal(Tl) detector used for routine counting is enclosed in a 2 -in lead brick

shield. A second 3 in x 3 in Nal(Tl) detector shown immediately above the lead shield in figure 8 may be used together with

the first detector for gamma-gamma coincidence counting upon

removal of the roof of the shield. For further details see

the experimental section below.

(D. A. Becker and G. W. Smith)

15
Figure 7. Radiochemical hood and counting equipment

in the NRL radiochemistry laboratory

OFFICIAL UNITED STATES NAVY PHOTOGRAPH

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5. Digital Computer Facilities

The common facility that has an extreme impact on the

function of all of our projects is the digital computer

facility. We are continuing to emphasize the use of the

multistation approach and find that this system is the most

practical for our purposes. We are using the system described

in last year's report [1] with the exception that the computer

center is now located at the site of a computer service center

in the Washington, D. C. area. One problem which occurs with

the multistation teletype console use is the data transmission

time. At ten characters per second the transmission time for

large numbers of gamma-ray spectra can amount to hours per day.

The use of a leased-line Tel-pak installation can remove this

problem since transmission in the ten-kilohertz range can be

realized. Costs for a central data transmission system of this

type are not excessive. From the user T s point of view, the

computer is thus brought into the laboratory and is immediately

available. Not only is this extremely valuable in getting the

computing work done, but it tends to stimulate ideas on how

experiments can be better accomplished to make use of this

rapid calculating ability.

a. Least Squares Calculations . We have programmed

the computer to do a variety of calculations of interest in

activation analysis. Among the most useful of these computations are those of least-square solutions. Program GAUFIT

utilizes the procedure described by Robinson [5] for fitting

a gamma-ray photopeak to a Gaussian distribution by an iterative least-squares approach. Another program has been written

to analyze complex decay curves. We are currently inserting

the procedure described by dimming [6] for iterative determination of the decay constants. We have programmed the computer

to fit complex gamma-ray spectra with up to 50 subgroups using

up to nine standards.

b. Other Computations . The computer has been programmed to do spectrum stripping. This stepwise analysis is

18
particularly suitable for the time-shared computer system, as

the almost conversational communication between user and computer allows for detailed examination of the analysis as it

proceeds.

We have programmed the computer to do a variety of other

calculations such as plotting data, selecting optimum time for

irradiation and decay in an activation analysis, maintaining

inventories of radionuclides, gamma-ray photopeak integration

with correction for decay and normalization to flux monitors,

and correcting for flux perturbation during an irradiation.

(G. J. Lutz and J. R. DeVoe)

B. Analyses with Nuclear Reactor

1. Determination of Copper in Standard Reference Material

82b N i eke 1 - Chromium Cast Iron by_ Gamma -Gamma Sum Coincidence Spectrometry

a. Introduction . The element copper is often easily

determined as a minor constituent in an iron matrix by the

neutron activation analysis technique. However, it was found

that this particular sample presented a number of problems.

Nickel -chromium cast iron Standard Reference Material SRM 82b

contains a total of eleven elements, with 1.2% nickel and 0.75%

manganese along with the 0.03%. copper (table 1).

Conventional nondestructive neutron activation analysis for

copper in this matrix is beset with difficulties. Two copper

radioisotopes are available for use, copper-66 and copper-64.

The copper-66 radioisotope (5.1 min T, /«) cannot be used because

of low sensitivity and interference of the 1.11-MeV gamma ray

from nickel-65, as well as the large amount of Compton

continuum background due to the 1.81-MeV gamma ray from man-

; ganese-56. The copper-64 radioisotope (12.9-h T^) by itself also would give extremely poor results, since the 1.34-MeV

gamma ray is of very low abundance and the 0.51-MeV gamma ray

from positron annihilation coincides with the Compton edge from

0.85 MeV gamma ray of manganese-56. In addition, the manganese56 radioactivity produced by a short irradiation (10 minutes)

19
is more than 840 times that due to copper -64. In fact, the

total radioactivity of the sample compared to the copper is

such that the copper is almost completely obscured in the gammaray spectrum (figure 11). These conditions indicate the need

for a radiochemical separation of the radioactive copper from

the balance of the interfering radioactivity. However, such a

separation is difficult and time consuming. Also these iron

samples contain a relatively large proportion of carbon and

silicon (table l) which are almost impossible to bring completely into solution.

The best possible answer to this predicament would be the

use of a rapid, simple instrumental method of discriminating

against all other interfering radioactivities and to count only

the copper-64 radioactivity. The technique of gamma-gamma sum

coincidence spectrometry is such an instrumental technique.

The detection of positron annihilation is well suited for sum

coincidence spectrometry, since the 180° angular correlation

of the annihilation radiation virtually assures that two

3 in x 3 in Nal (Tl) scintillation detectors in close geometry

Table 1. Approximate composition of SRM 82b,

nickel -chromium cast iron

Element

Iron

Carbon

Manganese

Phosphorus

Sulfur

Silicon

Nickel

Chromium

Vanadium

Titanium

Copper

20

Concentration

(% by weight)

92 ,7

2,.8

0.,75

0.,022

0.,007

2. 10

1. 2

0. 33

0. 023

0. 024

0. 03
will detect both 0.51-MeV gamma rays from a high percentage of

the positrons emitted. Such a coincidence arrangement discriminates against all other radioactivity except radioisotopes

emitting positrons or gamma rays in cascade. In addition, by

setting the threshold level at 0.3 MeV, all radioactivity

except gamma rays between 0.3 and 0.9 MeV is discriminated

against for the gamma-ray region of interest (0.8 to 1.2 MeV).

As a result of the above instrumental discrimination in favor

of the positron annihilation radiation, it was expected that

the 1.02 -MeV sum coincidence peak could be isolated with minimal interference from other matrix radioactivity. Possible

interferences by long-lived positron emitters formed by the

highly probable (n,y) nuclear reaction include zinc -65, cadmium-107, antimony-122 , and europium- 152m. These elements

were known to be below detection in the sample under analysis.

b. Instrumentation . A schematic diagram of the sum

coincidence spectrometer is shown in figure 9. Two opposed

3 in x 3 in Nal(Tl) scintillation detectors with associated

sample holder were used to position the sample precisely between the centers of the two detectors, and as close to the

detectors as possible (for high efficiency). The anode output

from the photomultiplier tube on the detector goes directly

into the summing preamplifier. The preamplified last dynode

output leads into the B and C inputs of the coincidence resolver and routing unit. Then, when properly connected as shown

in figure 9, the sum coincidence pulses are emitted from the

blocking output of the re solver and channeled into the 0-99

subgroup of the multichannel analyzer. The noncoincident

pulses enter the 100-199 (B detector) and 200-299 (C detector)

subgroups of the analyzer [1].

The prompt coincidence electronic circuitry used had a

slow (2 /^s) resolving time. Faster resolving times were not

necessary since discrimination of nuclear transition times

was not of interest in this application. The prompt coincidence analyzer drives the delayed coincidence input of the

21
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COINCIDENCE

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EXTERNAL

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Figure 9. Gamma -gamma sum coincidence spectrometer

22
multichannel analyzer due to the two microsecond resolving

time logic of the coincidence analyzer. This coincidence logic

is appropriate for the time constants associated with sodium

iodide detectors and the counting rates encountered in this

work.

c. Experimental . The samples of nickel -chromium cast

iron granules were held in the base of a polyethylene snap-cap

vial (3/8 in diameter) by means of cellulose paper (figure 10).

This vial was forced into a Lusteroid test tube for counting.

The tube fit snugly into a polyethylene and bakelite sample

holder, which reproducibly positioned the sample in the geometrical center of the two opposed detectors.

Several preliminary irradiations were made to compare the

standard nondestructive activation analysis techniques with the

proposed sum coincidence technique. After concluding that the

analysis could be done nondestructively using the coincidence

technique, a series of irradiations were made on samples of

100 mg to 500 mg in size to determine the effects of neutron

shielding.

The actual analysis was accomplished with both samples and

standards individually packed in polyethylene snap-cap vials.

The samples consisted of accurately weighed quantities of the

nickel -chromium cast iron (approximately 500 mg) tightly forced

into the bottom of a vial with cellulose tissue. The configuration of the sample was essentially a disk with a diameter

of 9 mm (the inside diameter of the polyethylene vial) and a

height of about 3 mm. The standards consisted of 25 to 50

microliters of a copper solution (analyzed reagent grade copper,

99.9+%) placed on several layers of heavy filter paper in the

bottom of a snap -cap vial and allowed to dry. This produced a

standard with very close to the same geometrical configuration

as the samples. The standards were then packed with cellulose

tissue to prevent movement in the vial. Blank snap-cap vials

with tissue and filter paper were made to determine the copper

^content of these materials. Copper foil flux monitors were

23
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LUSTEROID

TUBE

DEAD

STOP

/ SPACERS TISSUE SAMPLE

POLYETHYLENE

Hrd^f £

XT,

SNAPCAP_VIAL

V

Figure 10. Sample positioning with respect to the detectors

attached to the base of the samples, standards, and blanks to

normalize for neutron flux. They were then each irradiated for

11 -2 -1

15 minutes at a thermal neutron flux of 8 x 10 n«cm s in

the north pneumatic tube terminal of the NRL nuclear reactor,

allowed to decay for one day, and then counted for 12 minutes

in the sum coincidence spectrometer as described above. The

flux monitors were counted after two days decay for 1.2 minutes

using standard gamma -ray spectrometry. The gamma-ray peaks

due to copper-64 from the spectra of the samples, standards,

and flux monitors were integrated and corrected to zero time.

24
d. Results and Discussions . The results of preliminary irradiations may be found in figures 11 and 12. Figure 11

depicts the normal gamma-ray spectrum of the nickel -chromium

cast iron after 20 hours decay with the discriminator set at

0.3 MeV. The overriding radioactivity present is manganese-56

,

with the 0«51 MeV gamma ray from copper-64 almost completely

obscured by the manganese Compton edge. Figure 12 shows the

gamma-gamma sum coincidence spectrum of the same sample at i approximately the same time. In this figure the 1.02 MeV

sum peak from copper-64 is the primary radioactivity present

and may be easily determined nonde struct ively with simple

integration of the gamma -ray peak. The results of preliminary

irradiations to determine the effect of sample size on any

potential neutron self-shielding showed no significant difference in the relative copper concentration between the 100 mg

and 500 mg samples. In addition, computer calculations on the

neutron attenuation expected with the nickel -chromium cast

iron predicted about 2% for a 100 mg sample and 3%, for a 500 mg

sample.

The results of the determination of copper in nickel-chromium cast iron are given in table 2. Nine analyses were made on

different 500 mg samples. The average determined was 0.0317

±0.0002% copper (± value is the S^ of the average). The values

determined by the NBS wet chemical method [7J averaged 0.0376

±0.0007% copper; the values obtained by the NBS industrial

cooperators were 0.036% and 0.035% copper. These other values

averaged 14% above the results for activation analysis, which

suggests a negative bias in the activation analysis results.

Subsequent investigation revealed the presence of such a negative bias due to gamma-ray attenuation in the sample. The

preliminary irradiations of samples of different sizes was

intended to reveal just such a bias. However, due to the

peculiar configuration of the counting technique, the gamma -ray

attenuation was not affected by sample size, but was relatively

25
DECAY TIME: 20 HOURS

COUNTING TIME: 10 MINUTES

GAMMA RAY ENERGY(MeV)

Figure 11. Normal gamma ray spectrum of SRM Cast Iron 82b

26
8

h-2

3O

2 -

DECAY TIME: 20 HOURS

COUNTING TIME: 10 MINUTES

64Cu SUM COINCIDENCE PEAK

1.02

GAMMA RAY ENERGY (MeV)

Figure 12. Sum coincidence spectrum of SRM Cast Iron 82b

27
Table 2. Results of Activation Analysis

for copper in SRM 82b

Sample Copper

No. concentration (%)

a

0093 0.0319

0094 0.0321

Sample

weight (mg)

507.3

514.1

510.1

500.8

510.7

502.7

0095 0.0327

0096 0.0324

0097 0.0324

0098 0.0314

0101 0.0310 511.9

0102 0.0309 508.8

0104 0.0316 509.6

Average = 0.0317 ±0.00022% copper b

a Note discussion on negative bias in text.

± value is the SD

of the average.

constant for all samples. This anomaly results from the effective sample shape of a disk, with the plane of the disk parallel

to the axis of the detectors. Thus, the effective thickness of

the sample is the diameter of the snap-cap vial, which is nine

millimeters. This effective thickness remains the same whether

the sample weight is 100 mg or 500 mg. Very rough preliminary

experiments on the gamma-ray attenuation expected in such a configuration gave a value of about 10%, which is of the same order

as the negative bias found in the results when the neutron selfshielding is included. This problem of gamma-ray attenuation,

which has also been experienced in several other analyses, is

being examined much more thoroughly. A change in the sample

orientation and/or the determination of an accurate correction

term should allow this gamma-gamma sum coincidence technique to

be used for simple interference-free nondestructive activation

analysis of copper in most matrices.

(D. A. Becker and G. W. Smith)

28
2. Homogeneity Testing by Neutron Activation Analysis : Determination of Homogeneity of Dissolved Metal

Chelates in Military Metal-in-Lubricating Oil Standards

Testing for sample homogeneity usually requires a survey

analytical technique. This is because most homogeneity testing

requires rapid multiple element high precision analyses. Neutron activation analysis is not normally used as a survey instrument, since many matrices and/or components produce interferences which require tedious and time consuming radiochemical

separations. However, nondestructive neutron activation analysis does permit rapid multiple element analyses in some samples.

The requirements are that the element (s) of interest be determined nondestructively and that the induced radioactivity from

the matrix or other components does not significantly interfere

with the determination. This noninterference may result either

from a low induced radioactivity level or a significantly

different half-life.

The above conditions were met recently when the NBS Standard Reference Material Program required homogeneity testing

of some metal-in-oil standards. These standards consist of ten

metal chelates dissolved in a viscous lubricating oil (50 SAE)

at nine different concentration levels. The metals were aluminum, copper, nickel, iron, chromium, silver, tin, magnesium,

lead and silicon at the concentration levels of 1, 3, 5, 10,

30, 50, 100, 300, and 500 parts per million, respectively.

These standards were to be used by the Defense Department in

calibrating analytical instruments for the determination of

engine wear in military aircraft by the analysis of their lubricating oils.

Since the organometallic chelates required a relatively

high temperature for dissolution in the oil, due to their low

solubility at room temperature, several questions arose concerning the homogeneity of the metals in the oil at room temperature

both immediately after cooling and at the end of the .r estimated

shelf life of six months. These questions involved deviations

29
from homogeneity caused by possible precipitation or colloid

formation, by incomplete dissolution or mixing, or by subsequent formation of concentration gradients in the oil solution

due to density variations.

The Activation Analysis Section was requested to make a

survey of the relative concentrations of several elements in

these metal-in-oil standards. Difficulties would be experienced in the use of most survey analytical methods in the

analysis of a viscous hydrocarbon oil, especially at the lower

concentration levels, but this matrix is ideal for neutron

activation analysis due to the extremely low radioactivity induced by the matrix. The elements chosen for the analysis were

the two most sensitive for a short irradiation and decay time,

aluminum and copper. These two elements are chemically very

different and should adequately represent the metals added to

the lubricating oil. In addition, their decay schemes indicate

that they can be determined in the presence of each other. The

aluminum has a short half -life (2.3 minutes) with high energy

gamma ray (1.78 MeV) and may be counted immediately after irradiation with no interference, using a gamma-ray scintillation

spectrometer. The copper-64 has a relatively long half-life

(12.9 hours) and the 0.51 MeV gamma ray produced by its positron annihilation may also be determined (after decay of the

aluminum) with minimal interference using a gamma-ray scintillation spectrometer. Metal in oil concentration levels of

1, 50, and 500 parts per million were analyzed.

a. Experimental . The samples were prepared for irradiation by completely filling a small precleaned polyethylene

snap -cap vial (2/5 fluidram size; capacity about 1.5 cm [1, p26]

with the lubricating oil, attaching a copper foil flux monitor

in reproducible geometry, and sealing in a NRL polyethylene

rabbit. The samples were then individually irradiated in the

north pneumatic tube irradiation position in the NRL Reactor

11 -2 -1

at a thermal neutron flux of 8 x 10 n»cm s [1, p45] .

30
The irradiation times were 1 minute for the 50 and 500 ppm

levels, and 10 minutes for the 1 ppm level. By use of the

pneumatic tube delivery terminal just outside the radiochemistry laboratory, the total decay time between the end of the

irradiation and the start of the aluminum count was limited to

1.5 minutes. This interval included removal of the copper foil

flux monitor (with storage of the monitor behind four inches of

lead) and transfer of the lubricating oil to a clean tared polyethylene snap-cap vial. The vial with oil was then reweighed

after counting in order to determine the exact amount of oil

present when the sample was counted.

The counting equipment utilized was a 3 in x 3 in Nal(Tl)

scintillation detector and 400-channel pulse height analyzer.

The counting conditions were kept constant for each element and

each concentration level, but varied among groups. The distance

from the sample to the detector varied from 0.5 to 10.5 cm.,

which gave some control over the count rate seen by the detector. Total peak counts accumulated averaged 100,000 for the

higher concentration levels and 15,000 for the 1 ppm level.

b. Results and Discussion . Preliminary irradiations

showed no significant radioactivity in the pure lubricating oil

(before addition of the metal chelates). Also, irradiation of

the oil containing the chelates showed no significant interference in the aluminum and copper gamma ray spectroscopy.

The results of the first homogeneity test are given in

table 3* These samples had been prepared less than one month

before analysis. After three additional months of standing,

a second test was made (table 4) . Values given in both tables

are "normalized Percentages" defined as:

Relative Concentration at a Sampling Level , ~ n Avg. Relative Concentration for 3 Sampling Levels

Tests for rejection of outlying observations were applied

to the values 96.7 and 97.3% in table 3 and 91.7 and 109.7% in

table 4 using the Dixon statistical criterion [ 8, pp. 17-3 to

31
Table 3. Normalized percentages of aluminum and copper in

military metal-in-lubricating oil standards - first sampling

Sample

No,

0106

0107

0108

0110

0111

0112

0113

0114

0115

0116

0121

0117

0118

0122

0119

0120

0123

0125

0126

0128

0129

0130

0131

0132

Concentration (ppm)

500

tt

it

TT

TT

TT

TT

TT

50

TT

TT

TT

TT

TT

TT

TT

1

TT

1

TT

TT

TT

TT

Sampling

Level

Upper

TT

Middle

TT

Lower

TT

TT

Upper

TT

Middle

TT

TT

Lower

TT

TT

Upper

TT

Middle

TT

Lower

TT

TT

Normalized Percentages

Aluminum

101.0

100.3

98.6

100.0

100.3

99.7

101.2

100.5

99.0

Copper

100.2

100.8

99.1

101.9

99.3

98.9

101.

6

a

96.

7

b

97.

3

C

, Cu sample 0125 only.

° Cu sample 0129 only.

Cu samples 0130 and 0131 only.

32
Table 4. Normalized percentages of aluminum and copper in

military metal-in-lubricating oil standards - second sampling

Sample Normalized Percentages

No.

Concentration (ppm)

Sampling

Level

0241

0242

0243

500

TT

TT

Upper

TT

TT

0244

0245

0246

t!

TT

tr

Middle

TT

TT

0247

0248

0249

Tt

TT

TT

Lower

TT

TT

0253

0255

50

TT Upper

TT

0256

0257

0258

TT

TT

TT

Middle

TT

TT

0259

0260

0261

50

TT

TT

Lower

TT

TT

0265

0266

0267

1

TT

TT

Upper

TT

TT

0268

0269

0270

ft

TT

TT

Middle

TT

TT

0271

0272

0273

TT

TT

TT

Lower

TT

TT

Aluminum

100.4

101.2

98.3

100.2

101.7

98.2

109.7

91. 7 a

98.6

Copper

100.0

100.9

99.0

100.0

102.5

97.6

100.2

97.1

102.7

Rejected value - See Text, p. 31,

33
17-5]. The population mean and standard deviation (<r) were

considered to be unknown. Using the method in the reference

cited, only the value 91. 7% was rejected at a level (a) of 0.05

probability. This is the probability that we would be rejecting an observation that really belongs in the group of data.

The "Fv- test for variability [8, pp. 4-8 to 4-9] was then

applied, comparing upper to middle, upper to lower, and middle

to lower in both samplings. At the 0.05 level of significance

(a) , no difference in variability was found between sampling

levels in either table 3 or table 4. This is a 95% confidence

interval estimate of the ratios of the true variances £=^r, etc.

between levels (e.g. A and B) of each sampling.

Mean values were calculated from the different sampling

levels in tables 3 and 4 and plotted in figure 13. It is appar

ent that the upper points differ from the lower points by 2.2%,

in the first sampling and by 2.7%> in the second. In order to

103-

102

LlI

cc

Q.Q

LlI N

o

101

100

99

98

(a)

_L UPPER MIDDLE LOWER UPPER

SAMPLING LEVE'

MIDDLE LOWER

Figure 13. Plot of averaged data from first (a) and second

(b) samplings with 95% confidence limits

34
determine if these differences were statistically significant,

a short test [8,p 15-5] was applied. In the first sampling, at

the 0.05 level of significance, the upper value was shown to

exceed the lower. In the second sampling, the upper level did

not exceed the lower at the same level of significance. Because

this short test might result in "an error of the second kind,"

that is, not show a difference where one exists, more discriminating tests were applied. The first [8,pp 3-34 to 3-36],

which assumes that the variability between levels is unknown

but equal, and a second, "the method of pairs" [8, pp 3-38 to

3-40], both showed that the upper value did not exceed the

lower, at the same 0.05 significance level.

The plot of the data (figure 13) shows the 95% confidence

limits for each point representing a mean, and the lines drawn

are estimated by eye. For no known reason, the confidence

ranges of the points in the second sampling are wider.

The second set of samples also included a composite sample

at each concentration level, composed of one third of each level

mixed together. The results from the composite samples are

compared with averages of each level in table 5. They show

relative concentrations which vary from the average of the individual samples. This may be due to incomplete mixing or

sampling problems.

c. Conclusion . The results indicate a slight inhomogeneity in the metal in lubricating oil standards. That the

tendency should be to rise instead of settle is not surprising

since the density of the metal chelates is less than the density of the pure oil.

Upon consultation with T. W. Mears and C. L. Stanley, who

prepared the oils, it was found that the difference in homogeneity is within the limits of precision of the analytical

technique used (emission spectrographic analysis). Data from

two Armed Services laboratories showed that "within laboratory"

precision (based on successive triplicate determinations on the

35
Table 5. Comparison of aluminum and copper composite

samples with averages for same elements at 1, 50, and

500 ppm. (Data in Normalized percent)

Aluminum Copper

Concentra- Avg of Avg of

tion (ppm) Composite Levels Composite Levels

500 102.3 100.0 102.1 100.0

50 98.2 100.0 97.7 100.0

1 114.9 100. a 92.8 100.0

a Assumed to be 100.0. Value of 91.7 rejected by Dixon

statistical criterion.

same sample) varied from ±5 to 10% standard deviation in 5 out

of. 6 cases,* for the levels 3, 50, and 500 ppm. It is therefore believed that the homogeneity as determined is sufficient

for the purpose outlined.

(D. A. Becker and G. W. Smith)

3. Fast Neutron Activation Analysis

a. Introduction . Activation analysis with 14 MeV

neutrons offers certain attractive features absent in thermal

neutron activation work; for example, bulk matrix interference

from (n,y) products, and the possibility of second order reactions are almost completely eliminated. In this respect, analysis with reactor spectrum neutrons generally suffers seriously

since many samples contain large amounts of sodium and chlorine.

Depending upon the particular element under consideration,

14 MeV neutron activation offers a choice of nuclear reactions,

any one or all of which could be used in the optimization of

the analytical procedure. In general, three predominant reactions can be induced, i.e., (n,p), (n,a), and (n,2n). In the

light elements, the appropriate selection of a reaction considerably simplifies their determination. The elements, 0, F, N,

One set of aluminum determinations at the 500 ppm level had

a precision of ±27o standard deviation.

36
Al, and Si, are in this category. Recent developments in the

field of 14-MeV neutron activation analysis indicate that this

approach lends itself extremely well to the interference-free

determination of oxygen at concentration levels below 100 ppm.

1 ft 1 ft The analysis is both rapid and nondestructive. The 0(n,p) N

reaction is utilized, and only those gamma pulses exceeding

4.5 MeV are recorded. The entire analysis is instrumental and

is completed within two minutes. i Considerable interest in the oxygen content of metals has

been indicated by industry. Therefore, a number of standard

reference materials have been analyzed for oxygen by analytical

techniques other than neutron activation analysis. These are

carbon steels (SRM 1041, 1042, 1044, 1045), ingot iron and low

alloy steels (SRM 400 and 1100 series) and other nonferrous

samples of interest which include some of the titanium-based

alloys. These standard reference materials have oxygen content

varying from 0.003 -0.1%.

The metal standards described above impose strict criteria

which suitable analytical techniques must satisfy. For instance,

it is desirable to express oxygen at the 30 ppm level to within

±5% standard deviation of a single determination. Accuracy

should be within the precision limits.

A survey of literature on the subject reveals the great

interest that has recently been generated in the search and

development of precise and accurate analytical methods for oxygen. A number of nonnuclear methods, e.g. vacuum fusion, inert

gas fusion, etc. , although capable of high sensitivities (<5 ppm

0) suffer from inaccuracies due to incomplete oxygen recovery

from the sample matrix. Analytical techniques utilizing 14 MeV

neutrons are found to be good to approximately 20 ppm oxygen in

dense samples. However, there is a definite deficiency in the

evaluation of certain nuclear measurement characteristics like

flux depression parameters and gamma attenuation factors which

directly affect the accuracy of the technique. In addition,

nonhomogeneity of samples introduces further errors. Our

37
approach to these problems is being directed toward a detailed

study of the effect of flux depression and gamma attenuation in

thick samples in an effort to perfect a technique fully satisfying the accuracy requirements of the Standard Reference Materials

Program. At the peak flux capacity of the neutron generator

it is hoped that oxygen determinations will be feasible at the

100 ppm level and possibly lower with high precision and

accuracy.

b. Planned Experimental Approach for Oxygen Analysis . The inherent nonhomogeneous and nonuniform nature of fast neutron fluxes as obtained from neutron generators has been the

prime factor governing the design and construction of a suitable target assembly. Previous research has indicated that

considerable improvement in reproducibility of analysis can

be made if samples could be rotated. A target assembly which

allows irradiation of both standard and unknown while rotating

around two different and perpendicular oriented axes is being

considered. Certain features associated with this target design

will allow direct determination of correction factors resulting

from flux depression and gamma attenuation with a high degree of

precision. These correction factors can then be applied to noramlize the oxygen activity generated in an unknown sample to

that in a basic laboratory standard. Benzoic acid (SRM 350) is

one of several primary standards being considered.

In the past, the nonavailability of sample containers of

low oxygen content has been a limiting factor insofar as the

sensitivity of the analysis is concerned. In an effort to improve upon this situation, we have recently acquired a limited

number of polyethylene snap-cap vials moulded under a nitrogen

atmosphere. Hopefully, the oxygen content of such vials will be

at least two orders of magnitude less than those in current use.

The new vials will be evaluated carefully for both absolute magnitude and variability of oxygen content. Due precautions will

be taken to exclude oxygen during sample preparation and

38
irradiation. The pneumatic transfer system has the capability

of operating in a nitrogen atmosphere.

Special sample preparation techniques will be explored.

The variation in oxygen content resulting from surface treatment will be studied. Efforts will be directed toward standardized encapsulation and treatment of samples prior to

analyses.

c. Summary . The main emphasis in this program will' be

placed on the development of a precise and accurate technique

for oxygen analysis in metal samples. Standard reference materials certified for oxygen (particularly steel) are of vital concern for use in calibration of the available methods. Umpire

calibration of such methods is a key factor in obtaining high

quality steels. It is hoped that the fast activation facility

will contribute in this area of interest, and provide answers

to questions of great importance not only to industry but also

to the analyst interested in oxygen analysis of high precision

and accuracy. Experience gained during this program will broaden the scope of this facility so as to incorporate analysis of

other light elements such as F, N, Si, Al, etc., and at the

same time allow certain fundamental nuclear studies associated

with cross section measurements and fission to be pursued.

(S. Nargolwalla and G. W. Smith)

4. Production and Use of Copper Foil Flux Monitors for

High Precision Neutron Activation Analysis Utilizing

Short -Lived Radioisotopes

a. Introduction , in the NBS neutron activation analysis program utilizing the NRL Nuclear Reactor, several problems

were encountered which preclude the simultaneous irradiation of

sample and standard. First, there is a large flux gradient in

the pneumatic tube terminal irradiation position (vertically

0.687o/mm; horizontally, 0.37%/mm) [1, p 46]. Thus, even if

irradiated together, the sample and standard would not be in

39
the same neutron flux. Second, once in the pneumatic tube,

no control can be exercised over the rabbit as to orientation

to the high flux side. It is then not known a priori in which

direction the horizontal flux gradient occurs and as a result

a correction could not be applied. Third, many of the analyses

for the Standard Reference Material Program either require or

are most easily accomplished by the use of short half-life

radioisotopes (e.g., 2.3 min 28A1, 3.7 min 52

V, 18 s 77mSe,

19 s ""Hf) which decay too rapidly for the standard to be

counted with the sample. To overcome these problems, a system of flux monitoring was developed which would normalize

the fluxes encountered under the above conditions.

The element decided upon for the flux monitor was copper.

The copper-64 radioisotope of this element has a 12.9-h halflife with a high abundance 0.51 MeV gamma-ray from its positron annihilation [9]. It can thus be counted at any time up

11 -2 -1

to 2 days after a 20-second irradiation at 8 x 10 n»cm s This allows the immediate concern to be focused on the sample

counting. However, the half -life is short enough so that prepared monitors may be reused after several weeks decay. In

addition, copper is exceptional in that its neutron activation

cross section is practically linear with energy with no large

resonance peaks [10]. The relative copper activation for any

neutron flux will then closely approximate the activation of

the majority of the elements to be analyzed. Elements which

have a high resonance integral (activation or absorption)

should either use a flux monitor of the same element (standard)

or careful control must be exercised over the neutron energy

distribution during the irradiations. Many of the most commonly used flux monitors actually have very high resonance integrals or absorption peaks, and therefore should only be used

with caution when the element of interest does not have a

corresponding neutron absorption cross section (table 6).

40
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41
The physical and chemical properties of copper are also

excellent for this application. Copper is readily available

in pure form (99.9%, reagent grade) as a foil and is quite

inexpensive. It is relatively ductile, does not corrode in the

usual laboratory atmosphere and will dissolve easily in concentrated nitric acid if an aliquot is desired. In addition,

copper may be easily alloyed with pure lead, to form a dilute

alloy for monitoring a high neutron flux. The alloy concentrations of 1% Cu-in-Pb and 0»1% Cu-in-Pb have been successfully

produced and rolled into approximately 5 mil foils using a

simple hand rolling mill.

b . Production and Use of Copper and Copper -Lead Flux

Monitors . The copper foil used was reagent grade foil from a

laboratory supply house, obtained in 5 mil thickness. A 3/16-in

diameter paper punch was used to obtain disks which weighed

approximately 20.5 mg each. These pure copper foil disks were

then mounted on a suitable base material (cardboard, cellulose

tape, or plastic) with cellulose tape (figure 14a). Tests

showed no significant 0.51 MeV radioactivity from these base

materials for an irradiation period of up to 30 minutes at a

11 -2 -1

neutron flux 8 x 10 h«cm s . The copper- lead alloys were prepared by placing the proper

weight of copper foil and reagent grade lead into a covered

vycor crucible and by strongly heating with a gas-oxygen torch

for several hours. Occasional mechanical mixing was also done

with a vycor stirring rod. After thoroughly alloying the metals,

the alloy was poured into an appropriate mold to produce a small

ingot. Each ingot after annealing was rolled into a foil

approximately 5 mils thick using a small hand, rolling mill.

The foil was then cut or punched into a suitable sample size

using a scissors or paper punch. These foil disks may then be

fixed on a suitable base material or left as prepared for affixing to the sample container. The cardboard as used for the pure

copper foils was not a suitable base material for the copper42
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43
lead alloy monitors, since upon irradiation in the higher neutron flux it contributed a significant fraction of the total

radioactivity formed. Several thicknesses of cellulose "magic

mending" tape seem to contribute no radioactivity in the gammaray region of interest, however. The use of a base material

(or tape encapsulation) does permit easy reuse of the flux

monitor, and does permit easy marking of the monitor as to

identification and monitor weight.

The absolute copper content of the alloy need never be

determined if the comparator technique is used for the actual

analysis. Once it has been established that a good alloy has

been produced, the weight of the alloy gives the relative

amount of copper present in the flux monitor. In this case

the same alloy should be used for a given series of determinations.

Use of the flux monitors, once they are prepared, entails

affixing them to the sample (standard) container as desired.

In this work, the samples and standards were encapsulated in

polyethylene snap -cap vials (figure 14b) [1, p 26] which have

a flat, circular bottom of 3/8- in diameter. Cardboard base

material was used for the copper foils, with the 3/16 -in foil

disk exactly centered in the middle of the 3/8 -in diameter

cardboard disk and kept there by cellulose tape. Then, by

fixing the cardboard monitor to the base of the vial, as shown

in figure 14, the foil flux monitor is held securely in position exactly in the center of the vial base and up against the

base. The monitor may be held in place with a narrow strip of

cellulose tape , leaving a tab on one end so that the tape

,

monitor, and base may be quickly removed from the sample. Using

this technique it was possible to begin counting a sample only

30 seconds after the end of the irradiation.

c. Results and Discussion^ The results of the use

of these foil flux monitors are found in table 7. Sample A

gives the reproducibility of the counting technique exclusive

44
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45
of sample, which seems to be about 1.6 times the counting statistics. In Sample B, the reproducibility decreases slightly

due to monitor repositioning. However, this increases the

relative standard deviation (SjJ to only two times that due to

counting statistics. In Sample C, the reproducibility decreases

by a factor 4.2 times the counting statistics - probably due

in large extent to an inherent error of about 0.57o in the

weighing procedure used, since a micro- or semimicro-balance

was not available and an analytical balance was used. The

alloy foils (Sample D) show greater variation and give an average SD of 1.08%. Thus, the above data show that by using pure

copper foil flux monitors a precision of up to 0.59% S^ may be

obtained in experimental neutron activation analysis with short

irradiations. If the copper -lead alloy foils are used, this

precision decreases to about 1.08% S^. The poorer precision in

the alloy foils is attributed to inhomogeneity in the alloy composition.

Sample E gives experimental results of a series of pure

copper foil flux monitors irradiated for identical periods of

time under analysis conditions. It may be seen from the average

SD of 1.66% that the NRL reactor neutron flux is fairly constant

over short periods of time. However, the S^ range is from 0.58%

(very close to the 0.59% of groups of six foils irradiated at

the same time) to 3.87%. These data indicate that without some

form of flux monitoring, it is left up to chance to determine

the precision of the neutron activation analysis results. Thus,

the final decision as to whether or not the extra work of producing and using a flux monitor is necessary depends on the

type of analytical work that is to be done with the activation

analysis technique. If high precision quantitative neutron

activation analysis is desired, then a flux monitor of some

sort is definitely required with each sample; and if the element

itself cannot be used as a suitable flux monitor, copper in one

form or another seems to be an excellent compromise.

(D. A. Becker)

46
5. Resonance Neutron Activation Analysis

a. Introduction * In contrast to the usual radiative

capture (n,y) method of neutron activation analysis with thermal neutrons, it is possible to induce the same reactions in

the so-called resonance energy region. In the neutron energy

3

range between 0.1 and 10 eV, certain isotopes, usually above

Z = 30, show sharp, high intensity cross section peaks. In

principle then, by the use of substantially monochromatic be.ams

from a neutron spectrometer, a high degree of activation analysis selectivity should be possible. Such a technique is calculated to have an upper limit of about 20 eV, since the neutron

2 intensity falls off as 1/E , limiting the sensitivity. Because

in most cases the resonance peaks do not overlap, interfering

gamma -ray peaks from induced radioactivities will be minimized,

benefiting selectivity with certain elements as will be shown

below.

Using resonance data available [10,11] and a simplified

Breit-Wigner relationship [12], total resonance peak integrals

were calculated which revealed 20 stable isotopes with integral

cross sections of 300 to 3 x 10 barns. (Elements above atomic

number 83 were not considered, because of their radioactive or

fissionable properties). The relationship used in the calculation was

:

Total resonance peak integral (barns) =

! = 27rVsrn ry

P rE x 10" 24

o

where: g = statistical weight factor = 1/2, except when

1=0, then g = 1.

Tn = neutron scattering width (eV)

r

= neutron absorption width (eV)

r, = neutron total width (eV)

E = resonance energy (eV)

9

2. 2 _ ft 2 _ 4.12 x 10" 18

2tt ft - ~2 g47
ft= neutron wavelength (cm)

From these total peak resonance integrals and the neutron

flux as a function of energy, amounts of induced radioactivity

were calculated. Table 8 gives these values for induced nuclide

disintegration rates and major gamma-ray peak cpm per microgram

for 15 elements. Though the specific activities produced are

well below those induced in conventional thermal neutron activation [13], the peak counting rates exceed the usual minimum

of 10 cpm necessary for radioactivities over 1 hour in halflife [13].

More significantly, calculated signal-to-noise (gamma -ray

peak to gamma-ray background, for example) values were enhanced.

Enhancement is defined as the ratio:

S/N Resonance neutron activation

S/N Thermal neutron activation

Calculations were made comparing induced radioactivities (dps)

obtained for a minor constituent in a matrix, by conventional

thermal neutron activation and by resonance neutron activation.

It was assumed that background gamma-ray activity was subtracted,

and that in the enhancement calculation, all factors such as

detector efficiency, gamma -ray abundance and peak-to-total ratio

cancel out. For 1 ppm hafnium in oxygen (1 fig in 1.125 g H«0) , to form 19 s Hf and 29 s 0, the enhancement at saturation

3

was 2.4 x 10 . In the case of 1% of europium in lanthanum, to

give 9.3 h 152mEu and 40.2 h

140La after 24 hours of irradiation,

the enhancement was 23. These cases are typical of the range

of enhancement expected for the elements in table 8, depending

upon the matrix element.

On the basis of the above considerations it was decided to

carry out at the Naval Research Laboratory preliminary experiments to verify, by the use of indium and iridium foils, the

calculated induced radioactivity levels. This was to be a prelude to a later more detailed investigation at the National

Bureau of Standards Reactor.

48
Table 8» Resonance neutron activation, resonance integrals

and induced radioactivity

Resonance Calc. Radioactivity produced*

Target

Isotope

peak

energy

(eV)

peak res.

integral

(barns)

Induced

radioisotope

Half

life

per mi

(dpm)

crogram

Prin. y-rav

peak (cpm)

176Lu 0.143 9.2xl03 177 Lu 6.8d 6.8xl05 2.5xl05

151Eu 0.461 7.3xl03 !52-Eu 9.3h 7.0xl05

5 „ 3x10*

i 168yb 0.597 3.6xl04 169yb 32d 9.6xl03 64

191 lr 0.654 2.4xl03 192 Ir 74d 6.8xl04

2 . 3xl03

151Eu 1.055 3.7xl03 152mEu 9.3h 4.4xl04 2.3xl04

177Hf 1.100 3.5xl03 178nv,.p 4.3s 1.3xlQ4 6.0xl03

103Rh 1.257 IxlO3 104Rh 42s 2.8xl03 l.lxlO2

193 Ir 1.303 l.lxlO3 194 Ir 19h 7.6xl03 S.lxlO 3

115 ln 1*457 2.8xl03 116mIn 54m 2.2xl03 2-QxlO 3

185Re 2.156 2.6xl03 186Re 91h 5.6xl03 4.1xl02

165Ho 3.92 3.3xl02 166Ho 27. 2h 4.6xl02 84

169Tm 3.92 1.37xl03 170Tm 129d 1.92xl03 35

L81Ta 4.28 3.8xl02 182Ta 115d 274 18

L97Au 4.906 1.2xl0 3 198Au 2.7d 576 440

147 Pm 5.43 6.9xl02 U8Pm 5.4d 5xl02 2.5xl02

99

Tc 5.64 1.4xl02 100Tc 16s 116 87

178Hf 7.80 1.83xl03 179mHf 19s 6.8xl03 2xl03

152

sm 8.01 2.12xl03

.+ ml4

Sm

-2 -1 £ ,

47h 80 20

a T * -j « •»--? ^.^-> O A U ~. whichever is shorter. Also optimized by a factor of 5 to

probable improved NBS reactor conditions.

Calculated for parameters of principal gamma-ray (factors

such as peak-to-total ratio, branching ratio, fraction unconverted transmission in 164 mg Cm~2 absorber) using a 5 in x

4 in Nal(Tl) well-type detector.

49
b. Experimental . A neutron spectrometer is in operation at the Naval Research Laboratory under the direction of

R. Vogt in which beryllium, germanium, or other single crystals

are used to produce neutron beams of narrow energy ranges in

the 0.1 to 10 eV region and above. A generalized schematic of

the neutron spectrometer used is shown in figure 15.

Foils were irradiated in the neutron beam by holding in a

simple wooden jig with tape. Counting by gamma spectrometry

was done using a 400 -channel pulse height analyzer by means of

a 3 in x 3 in sodium iodide crystal. Irradiations were made on

foils of indium and iridium for periods approximating one halflife of the respective radioisotopes m

In (54 min T, /0 ) and

194 *-/*•

Ir (19 h Ti/o)* In tne case of indium, the count rate of

its major gamma-ray peak (1.27 MeV) agreed closely with the

value as shown in table 8, when normalized to probable NBS

reactor conditions, with corrections for neutron absorption.

The iridium value, based on counting of the 0.328 MeV gammaray, was low by a factor of 10, probably caused in part by

uncorrected gamma -ray absorption in the 2 -mil iridium foil.

CRYSTAL

aMa

'COLLIMATOR

'SAMPLE HOLDER

BF3 COUNTER

COUNTER

SHIELD

REACTOR

SHIELD

/" -COLLIMATOR

Figure 15. Schematic of neutron spectrometer

50
c. Conclusions . The preliminary results show promise

for a unique approach to a selective method of neutron activation analysis for 15 elements, in which the matrix interference

may be reduced to a minimum. It may be necessary, unless extremely thin large area foils are available, to predissolve

samples and use a thin layer of solution in 2 in x 2 in square

cells for the irradiation. Such an irradiation configuration

will avoid excessive neutron absorption at the sacrifice of

necessitating probable blank corrections. It might also be

necessary to develop a method of simultaneous standard (perhaps

internal) irradiation for flux normalization. In addition, use

of a pneumatic terminal at such an irradiation site can be

considered.

(G. W. Smith)

6. Special Analyses

a. Selenium in Standard Reference Material 1170

Selenium Steel . The analysis of a selenium steel chip was

undertaken by neutron activation analysis. The selenium concentration was about 0.37o , with about 0.78% manganese and five

additional elements present. The 17.5 s half life selenium-77m

radioisotope was chosen, since it would give a sensitive and

rapid analysis with little or no interference from the longlived radioisotopes formed from a very short irradiation.

Preliminary results showed a serious problem of gamma-ray

attenuation for the 160 keV gamma -ray energy, even with the

smallest practical sample size. To compensate for this, the

sample and standard were put into almost identical matrices.

For the sample, this consisted of dissolution and evaporation

to perchlorate salts with dilution to a known volume. For the

standard, a synthetic mixture of ferric nitrate and manganese

dioxide was dissolved, evaporated to perchlorate salts, a

known amount of pure selenium added, and diluted to volume.

This resulted in a selenium standard which contained almost

identical amounts of iron, manganese and selenium per unit

51
volume as the sample. The samples and standards were then encapsulated in polyethylene snap-cap vials. Copper foil flux

monitors were attached in reproducible geometry to the samples

and standards, and irradiated for 20 seconds in the pneumatic

tube facility of the NRL reactor. Immediate counting, which

was normalized for flux differences, gave a selenium concentration of 0.293 ± 0.003% (± value is SD

of individual value).

Although preirradiation chemical treatment can result in the

generation of a blank, no significant blank level was produced

by this procedure. NBS wet chemical results were 0.298% selenium (by SCU reduction, subsequent iodimetric titration) while

the NBS cooperators obtained 0.288% and 0.290% (iodimetric titration) and 0.2947o (gravimetric). The average of these other

analyses is 0.292,-% selenium, which compares very closely to

the activation analysis result of 0.293%. selenium. (This

analysis will be combined with several others and published in

a more complete form in the periodical literature.)

(D. A. Becker, G. W. Smith, and E. D. Anderson)

b. Aluminum in Standard Reference Material 14e Basic

Open Hearth Steel . The analysis for aluminum in almost any

matrix is difficult by most convenitonal analytical techniques.

It is especially difficult when the aluminum is present as a

minor constituent among eighteen other elements, and is partially present as refractory aluminum trioxide and aluminum

nitride. The analysis was requested to be done by rapid, nondestructive neutron activation analysis since the use of this

technique should overcome the above problems. The main difficulty in carrying out the activation analysis technique is

caused by the presence of 0.407o manganese in the steel. The

manganese-56 produced by neutron irradiation has a 1.81-MeV

gamma ray which coincides almost exactly with the 1.78-MeV

gamma ray from the aluminum-28. This requires decay curve

analysis which may be either instrumental or manual. The instrumental technique consists of complement subtraction (using

the pulse height analyzer) of all of the manganese activity

52
from the original spectrum taken immediately after irradiation.

The manual technique consists of taking two spectra, the second

after all of the aluminum radioactivity has decayed, and manually subtracting the integrated peak counts (corrected for

decay) to obtain the pure aluminum activity at the time of the

first count. Appropriate standards were made from pure aluminum with enough manganese added to precisely duplicate the

sample radioactivity. Copper foil flux monitors were used with

both samples and standards. The results gave values of

0.059q ± 0.0024%, aluminum by the manual technique and 0.0612

± 0.0008% aluminum by the instrumental technique (± values are

S^ of the average, number of determinations are 6 and 5, respectively). These results agree rather closely with the NBS

wet chemical results of 0.061% aluminum and the NBS cooperators T results of 0.0595% aluminum. (This analysis will be

combined with several others and published in a more complete

form in the periodical literature.)

(D. A. Becker and G. W. Smith)

c. Vanadium in Standard Reference Material 73c Stain - less Steel.. A stainless steel in the form of turnings was received for analysis of vanadium by neutron activation. The aim

composition of the steel was 0.032% vanadium, 12.8%, chromium,

0.367o manganese, 0.12%, copper and ten other elements each with

a concentration of less than 0.45%. The vanadium-52 radioisotope (T, / 2 - 3.7 minutes) must be used for analysis, and

this radioisotope is also formed from the nuclear reactions

52 52 55 52

Cr (n,p) V and Mn (n,a) V. Preliminary experiments

with pure chromium and manganese established that these elements in the concentrations present in this sample would contribute only negligible amounts of vanadium-52 radioactivity

to the amount formed by the (n,y) reaction on vanadium-51.

Approximately 100 mg samples were encapsulated in polyethylene

snap-cap vials with flux monitors attached. Standards were

made from commercial spectrographically pure vanadium metal

53
(99.77. pure) and encapsulated identically to the samples.

Analysis by the comparator technique yielded a value of 0.03307o

vanadium, which is significantly higher than the value of

0.0287, vanadium found by NBS wet chemical techniques. Extensive examination eliminated all but one probable source of error,

the standard. To check this, a large piece of polycrystalline

vacuum refined vanadium metal was obtained from the NRL Metallurgy Division (stated 99.95+7, purity) and some purified V

?

0,-

was obtained from Dr. John Taylor, of the National Bureau of

Standards Analysis and Purification Section. Standards were

made of each of these three vanadium sources and analyzed by

neutron activation analysis for relative vanadium content. The

vanadium from NRL was found to have the highest theoretical

vanadium content and was assumed to be 100% vanadium. Later,

NBS spectrographic analysis confirmed a metal impurity level

of <0.057>. Compared to this, the "spec-pure" vanadium (stated

99.77. purity) actually had a relative vanadium content of

98.67., and the ^2®^ (supposedly stoichiometric) had only 98.47,

V«0,-. However, this correction was not enough to resolve the

entire conflict with the wet chemical technique, so a second

analysis was made with the NRL vanadium standard using the

method of standard addition [14, 15, 16, 17]. In this technique, known amounts of vanadium standard solution are added

to the stainless steel chip samples and the solution allowed

to evaporate. This produces a standard which contains an amount

of vanadium equal to that added plus the amount contained in

the steel sample present. This added vanadium upon evaporation

is deposited upon the entire outer surface of the steel. Since

equal portions of the added vanadium should be located on

opposite sides of each piece of steel, the neutron and gammaray attenuation seen by the added vanadium should approximate

that seen by the vanadium in the interior of the steel particles. Then, when the varying amounts of added vanadium are

plotted versus the count rate, a straight line extrapolation

to zero count rate will give the vanadium content of steel

54
present in the sample. In actuality, the least squares analysis of twelve data points taken at five different total vanadium concentrations gave the value of 0.0326 ± 0.0008% vanadium

(± value is S D of least squares plot of data) , which compares

very favorably to the results from the comparator technique of

0.0330 ± 0.0003% vanadium (corrected for the standard vanadium

content; ± value is S^ of the average). Later results for this

steel by NBS cooperating laboratories gave values of 0.031 and

0.0284 ± 0.0003% vanadium, all by wet chemical oxidation-reduction titrimetry. Thus, a discrepancy still exists between the

wet . chemical and activation results, which cannot be explained

at present. (This analysis will be combined with several others

and published in a more complete form in the periodical literature.)

(D. A. Becker, G. W. Smith, E. D. Anderson)

d. Survey of Pure Titanium Metal . Neutron activation

analysis utilizing short half-life radioisotopes at times

requires the use of a flux monitor with a corresponding short

half -life. A sample of very pure titanium (advertised purity

99.999%,) was obtained from a commercial source for testing as

a flux monitor. Titanium should be especially suitable in this

respect since the only radioisotope produced via the (n,y)

nuclear reaction is the 5.8 minute titanium-51. In addition,

the neutron spectrum has a resonance absorption integral of

3.8 barns with no total cross section peak greater than 100

barns, which should preclude strong distortion of the total

titanium radioactivity by small changes in the neutron energy

spectrum. To check the titanium for impurities, two samples

(1.4 and 39.8 mg in weight) were cut off with a jeweler's saw,

etched in ultrapure nitric acid (triple distilled from quartz)

and irradiated for separate 12 -minute periods at a neutron flux

11 -2 -1

of about 8 x 10 ' n»cm s . The samples were counted on a

3 in x 3 in Nal(Tl) scintillation detector with associated

400-channel pulse height analyzer and the decay followed for

55
several days. The results showed a manganese impurity of about

0.5 ppm, and a very small gamma-ray peak at an energy of 0.44

MeV, probably due to gold-198. Neither of these impurities

should interfere with the primary gamma ray of 0.32 MeV from

the titanium-51 under the normal conditions of short irradiation

and short decay time before counting.

(D. A. Becker and G. W. Smith)

e. Determination of Impurities in Pyrolytic Graphite . Recently several publications have proposed the use of pyrolytic

graphite as an electrodeposition matrix for preconcentration in

neutron activation analysis [18, 19, 20, 21], which is a technique that shows promise. Since its usefulness is limited by

the purity of the graphite matrix, it was decided to look at

the impurity levels of contaminants in a pyrolytic graphite

available to us. A sample (1/4 in diameter by 1/2 in long) was

obtained from Dr. R. G. Bates, of the Electrochemical Analysis

Section at NBS. The vendor of this graphite was Beryllium Corp.

of America, while the pyrolytic graphite used in the above referenced papers was obtained from the General Electric Corp. [21].

Two freshly cleaved samples were taken from the center portion of the graphite rod. The sample weights were 126.1 mg

(sample No. 1) and 151.0 mg (sample No. 2). Sample 1 was not

cleaned beyond fresh cleaving; however, sample 2 was etched in

ultrapure nitric acid (triple distilled in quartz) and rinsed

several times in distilled deionized water. Each were encapsulated in nitrogen-filled polyethylene snap-cap vials. The nitrogen atmosphere was necessary to reduce the adsorption of argon

from the air onto the surface of the graphite before and during

irradiation. Both samples were irradiated for 30 minutes at a

11 -2 -1

thermal neutron flux of 8 x 10 " n-cm s in the pneumatic tube

facility of the NRL nuclear reactor, and counted with a 3 in x

3 in Nal(Tl) scintillation detector and 400-channel pulse height

analyzer. Subsequently, the second sample was again cleaned in

ultrapure nitric acid and deionized water and reirradiated for

12 -2 -1

3.0 hours at a thermal neutron flux of 8 x 10 " n-cm s in

56
glory tube No. 1 of the NRL reactor. Sample handling and

counting was identical to that of the previous irradiations

.

The results of the determinations of impurity levels for

the unc leaned and cleaned pyrolytic graphite samples are found

in table 9. The uncleaned graphite (sample 1) contained sodium,

chlorine, manganese and an unidentified positron emitter in

significant quantities (figure 16). The irradiation of the

second (cleaned) sample at a similar neutron flux and irradiation time showed a reduced sodium and chlorine content of the

graphite. However, even with a cleaned graphite base, unless

the gamma-ray energy of the electrodeposited element (s) was in

an area of the gamma-ray spectrum free of background peaks , a

background subtraction as blank correction would be required

for the determination of small amounts of an element. The recieaned graphite sample (sample 2) when subjected to a longer

irradiation at higher neutron flux (3.0 hours at 3 x 10 n»cm~'

s~ ) produced significant amounts of radioactivity covering the

gamma-ray energy range of to 2.8 MeV (figure 17). In addition

to the sodium, chlorine, and manganese radioactivity present in

figure 16, the increased sensitivity reveals a relatively high

impurity level of tungsten in the graphite. The radioactive

Table 9. Impurity levels in pyrolytic graphite3

Concentrations found (ppm)

Element

Sample 1

(uncleaned)

Sample 2

(cleaned)

Sodium 13. 0.0016b

Chlorine 4.2 --n.d.

Manganese 0.023 0.0091

Tungsten --n.d. c 9.1d

Graphite obtained from Beryllium Corp. of America.

Identification verified by T, ,« determination of 14.0 h

2 ^Na.

Limit of detection estimated to be ~90 ppm tungsten.

Identification verified by T, /9 determinations of 21 h and

23 h for the gamma rays of 0.48 MeV and 0.69 MeV from xo/

W.

57
ioV

icr

{2 io

5

z

DO

(JCDO 2

-> 10

10 -

10

DECAY TIME: 20 MINUTES

DECAY TIME: 220 MINUTES

COUNTING TIME: 5 MINUTES

%C^X Mn 4.Ar

^

38

XV"*\ //A ~' •V1—^ A A A wV/' All

— A/ 1 |V l

i V

38

CI

A Na

/ \ *a

A

1 1

I

Figure 16.

GAMMA RAY ENERGY (MeV)

Impurity radioactivity in pyrolytic graphite,

sample 1.

tungsten-187 produced upon neutron irradiation has a half life

of 24.0 hours and abundant gamma rays from 0.07 MeV to 0.69 MeV

[22]. The presence of tungsten in the graphite is probably due

to containers of apparatus used in the manufacturing process.

Comparison of these values to the impurity levels to be

found in the pyrolytic graphite used by Bassos, et al. , is difficult, since they quoted no impurity levels and included only

one spectrum of the graphite [21]. However, from this spectrum

it is estimated that their impurity levels are about the same

58
10

8

\-

z

D

O 4 o

0.07

DECAY T IME : 105 MINUTES

COUNTING TIME: 300 MINUTES

I

Figure 17

I 2

GAMMA RAY ENERGY (MeV)

Impurity radioactivity in pyrolytic graphite,

sample 2 , second irradiation

as those found in the uncleaned graphite examined in this

study. In addition, unless their spectrum is mislabeled, the

presence of an aluminum-28 gamma-ray peak (T, /« =2.3 min)

after twenty minutes decay time would indicate an enormous

impurity of aluminum, which would be very detrimental to shortlived activation analysis.

(D. A. Becker and G. W. Smith)

59
C. Photon Activation Analysis Using the NBS LINAC

1. Introduction

The NBS LINAC is approaching completion. A rather extensive program in photon activation analysis utilizing the accelerator is planned. We will concentrate on those analyses for

which photon activation is extremely well suited. Analyses

which can be done rapidly, nondestructively by this method and

inconveniently by other methods will be investigated.

2. Meta-stable Isomers

A number of stable isotopes have meta-stable states with

half life adequate to be usable in activation analysis. These

states can be produced by inelastic scattering of neutrons,

photons and charged particles. If samples containing these

isotopes are irradiated with photons of energy below the

threshold for particle emission, the only radioactivity produced will be that due to the meta-stable isomers. Thus, one

has a potentially specific method for those elements which

exhibit this phenomenon. About twenty elements can probably

be determined this way. There is very little cross section

data available on these reactions, but experiments by other

workers indicate that one can analyze well below a microgram

for many of the elements of interest. Since these isomers are

induced by relatively low energy gamma rays, corrections will

be necessary for the photon flux attenuation in different

matrices. This will be a function of the composition of the

matrix and the energy level of the isomer.

3. The Light Elements

The elements carbon, oxygen, nitrogen and fluorine are not

analyzed well with thermal neutrons. This is due to very low

cross sections and because in all cases except fluorine, the

n,y product of the most abundant isotope is stable. In the

case of carbon and oxygen, sensitivity and reliability of other

analytical methods often suffer because of the blank problem.

60
The most serious problem in photon activation of these

elements is that their y,n products are positron emitters.

Since most elements yield positron emitters upon high-energy

photon irradiation, high precision analysis of the light elements without separation would not be very reliable in many

cases. In the case of carbon, nitrogen and fluorine, we would

expect to design a chemical separation after irradiation.

These separations would follow classical chemical methods used

in the determination of these elements. In the case of oxygen,

we will try to utilize either (y,2n) 14

or

18

(y,p)

17N

reactions. emits a 2.2 MeV gamma radiation and decays with

17

a 71 second half life. N emits delayed neutrons with a 4.4

second half life.

4. Other Analyses

There are many other analyses for which photon activation

should be very well suited. Among these would be the deterK / mination of magnesium by the reaction ' Mg (y,p) Na.

Although the sensitivity of this reaction is perhaps not

26 / 27 24

as high -as the Mg (n,y) Mg reaction, Na is a very convenient radioisotope to count and it would appear that this

reaction will be attractive for many magnesium analyses.

Iron is usually determined using the reaction ' Fe (n,y)

59 58

Fe. Because of the low abundance of Fe and the long half

59 life of Fe , this is not a very sensitive analysis. We hope

to improve the sensitivity of analysis for iron by utilizing

the reaction Fe (y,n) Fe. Fe has an 8.5 minute half

life. Chemical separation will normally be required.

The thermal neutron activation product of niobium is short

/ 92 lived and has a low energy gamma ray. The (y,n) product, Nb,

has a 10.1 day half life and an 890 keV gamma ray. A suitable

delay for the decay of shorter lived activities should allow

for the nondestructive determination of niobium in many samples

Many other potentially nondestructive analyses exist via

activation with a high energy bremsstrahlung beam. Judicious
selection of irradiation energy and time and utilization of

solid state detectors should allow the realization of these

analyS6S - (G. J. Lutz)

D. Experimental Design in Activation Analysis

1. Introduction

One of the general aims of the program in activation analysis is the planning of experiments in such a manner that sources

of systematic error may be recognized and eliminated insofar as

is practicable. The necessity for such a study becomes apparent

when one considers the increased sensitivity and improved

counting precision in activation analysis, due to the availability of more intense sources of bombarding particles or

radiation; accuracy has not improved correspondingly, for it

is often limited by factors other than counting precision.

One may attack the systematic error problem in a number of

different ways. For example, the experiment may be so designed

that certain types of systematic error do not arise. On the

other hand, statistical parameters which originate in the

treatment of the data may be used as guides to indicate the

presence and nature of possible trouble. Also, by means of

appropriate pre -experimental mathematical analyses, one may

plan an activation experiment so that it is best designed to

determine the component of interest.

In what follows we shall consider, first, methods for improving the accuracy of activation analysis in two important

respects: (1) the elimination of sources of systematic error

in chemical yield and detection efficiency by applying the

principle of T? over-all TT isotope dilution, (2) the correction

of external and self -absorption of gamma rays by means of a

semi -empirical treatment. Next, the use and interpretation of

an on-line computer program for analyzing mult i component decay

curves will be considered. Finally, radionuclide and detector

characteristics, together with the statistical aspects of

radioactive decay, will be considered in order to specify

62
"limits of detection" for given radionuclides in the presence

and absence of interfering radionuclides.

2. Elimination of Certain Sources of Systematic Error

a. "Over-all" Isotope Dilution , Systematic errors

may arise during chemical processing of a sample, if the

recovery is less than 100%; errors may also arise in the subsequent detection process if the (relative) counting efficiency

is not known accurately. Both sources of error may be minimized by an isotope dilution process whereby the "diluting"

isotope is added to the sample as early as possible - perhaps

even before irradiation - and is then detected along with the

radioactive activation product after chemical separation and

mounting have taken place. In this way the diluting isotope

may give an over-all measure of chemical yield and detection

efficiency, and thus serve to indicate quantitatively the

amount of the activation product originally present. The usual

precautions of isotope mixing and nonfractionation, of course,

apply. A major reason for the feasibility of the "over-all n approach is that for most elements there are available isotopes

which are not likely to be produced in the type of irradiation

planned, and that there are many powerful means for instrumentally discriminating between isotopes.

The principle of over-all isotope dilution is given in

equations (1).

R = AYE (la)

R

d =AdYEd

(lb)

A = (R/Rd )(Ed /E)Ad

(lc)

where R, A, Y, E represent counting rate, initial disintegration rate (activity), chemical yield, and detection efficiency,

respectively, "d" refers to the diluting radioisotope. Note

that A, need not be known absolutely; it may simply be referred

to an initial (pre -irradiation, prechemistry) counting rate

where the detection efficiency is fixed. Thus, as usual, the

chemical yield has no influence upon the results (unless it is

63
disasterously low). In addition, however, the necessity for

determining absolute detection efficiencies, and therefore one

possible source of systematic error, has vanished. In the simplest cases the relative detection efficiency, (E,/E) , may be

constant; then equation (lc) will take the almost trivial form,*

A = Const. • (R/Rd

) For example, with a number of types of radiation detector the

detection efficiency is proportional (or approximately proportional) to the solid angle. In such cases, the relative detection efficiency would be independent of changes in geometry,

except possibly for small corrections which could be determined

with far greater accuracy than corrections in absolute detection efficiencies. Other situations where the relative detection efficiency changes (for example, due to absorption effects)

are presently under consideration. Systematic errors in correction factors for relative efficiency are certainly smaller

than those in correction factors for absolute efficiencies.

The approach may be illustrated by the activation analysis

23 22 of Na with thermal neutrons, using Na as the diluting iso0*3 /

tope. Even a nanogram of Na will yield sufficient Na under

reasonable irradiation and counting conditions to yield a relative standard deviation due to counting of only 0.03%. It is

highly unlikely that chemical processing and counting will, in

general, lead to an accuracy commensurate with such an index

22 of precision. The utilization of Na, as outlined above, may

allow one to obviate systematic errors in recovery and detec22 tion efficiency which would otherwise be limiting. Na may

be added before irradiation, if desired, since it will not be

produced by thermal neutrons, and the two radionuclides may be

resolved by differences in half life or gamma ray energy.

Te The logical extreme of constant relative detection efficiency

occurs in the use of an "internal spike", where the same

radioisotope is added in order to determine the detection

efficiency. The diluting isotope may nearly serve this purpose as well as correct for lack of quantitative recovery.

Isotopes having similar energies but different half lives

may be the most desirable.

64
b. Accurate (y) Self-Absorption Corrections; A Semi - Empirical Approach , Systematic errors in the determination of

relative gamma emission rates may arise unless radioactive

samples and standards are counted under identical circumstances

or unless great care is taken to correct for differences in

geometry, external absorption and self-absorption. The corrections become more vital with increased solid angle, decreased

gamma energy, and increased sample and absorber density. One

approach to the problem would include a rigorous mathematical

treatment which considers, for each differential volume element

of the sample, the gamma peak efficiency resulting from an integration over all angles, and including the combined effects

of inherent peak efficiency and self- and external-absorption

for each differential solid angle. Such a calculation would

then be followed by integration over the total volume of the

sample. A similar calculation would have to be carried out

for each sample-type and location and gamma energy, and would

be far from trivial; a Monte Carlo approach probably would be

in order. At the other extreme, one might determine peak

efficiencies entirely by experiment. Such an approach, in

principle, would yield the highest accuracy, but it might be

limited by feasibility of preparing representative standards

for all configurations, energies, and sample-matrices of interest. As a reasonable alternative, an approximate treatment

has been pursued, in which the principle factors affecting the

peak efficiency are separated into "average" values, and in

which one or two semi-empirical parameters are introduced to

allow an accurate correlation with experiment.

Calculations have been made in which detailed consideration has been given to the effects of geometrical configuration upon external- and self-absorption of gamma radiation.

The effects of geometry on absorption and peak detection

efficiency have been related, in turn, to a "mean" sample

thickness, and all three factors (peak efficiency, external

absorption, and self-absorption) have been combined to give

65
a more accurate estimate of detection efficiency. The resulting formalism is quite simple: external absorption is given by

-vl / l-e'v ^' the factor, e~ ; self -absorption, by (—

-,—). J and /are

v x

dimensionless and represent the sample and absorber thicknesses,

respectively; and *v represents a geometrical correction factor

which depends upon / and /and upon the sample-detector configuration, v has been evaluated for a range of configurations

and thicknesses, using the GE-235 time-sharing computer.

In order to illustrate the above approach, absorption corrections have been estimated for aluminum and lead samples

,

each 4 mm thick, and located 2.5 cm and 11.5 cm (h) above a

7.6 cm x 7.6 cm-diam Nal detector having a 4 mm thick aluminum

absorber. For each location and each element two gamma energies were considered, 0.20 MeV and 1.00 MeV. Calculated values

for the external and self-absorption factors are given in

tables 10 and 11, respectively.

Table 10. External absorption factor (f

fl ) for aluminum absorber

h = 11.5 cmi h = 2.5 cm

0.20 MeV 0.874 0.844

1.00 MeV 0.934 0.918

Table 11. Self-.absorption

Aluminum

factor (f ) Lead

11,5 cm 2.5 cm 11.5 cm 2.5 cm

0.20 MeV .933 0.920 0.225 0.184

1.00 MeV 0,.970 0.958 0.852 0.820

To make the illustration more concrete one may estimate the

resulting detection efficiencies by including published values

for total and peak/total efficiencies [23]. For example,

A1U.00 MeV, 2. 5cm): Eff ^ £k.f

a

.f

s =(0. 0403) (0.918) (0.958)=0. 0354

Pb(0.20 MeV, 11. 5cm): Eff;s e^.f^f^O. 0230) (0.874) (0.225)

=0.00452

66
For highest accuracy, as stated above, the best approach

is to fix the conditions for calibration (counting of the

standard) so that they are identical to those for counting the

sample. Generally, this may best be accomplished by dissolving

the sample and counting the solution in a container which is

as similar as possible in size and location as that used for

the standard. If, however, varying configurations and sample

matrices are to be used - as, for example, in nondestructive,

activation analysis - it may be difficult to achieve exact

replication of sample and standard counting conditions. For

this reason a semiempirical approach, using the above formalism, seems desirable. Connection between experiment and theory

will be made by introducing an experimental normalization

factor a~. Normalization will take place using a convenient

sample -type and reference energy. Probably the most reasonable

choice for the sample will be a dilute aqueous solution of

specified volume and configuration. Small deviations from

the theoretical formalism with variations in Jc (sample size and

nature) or E (energy) may then be determined empirically for

variations about the reference point. One may find that relatively few observations away from the reference point will be

required, and that rather wide interpolation (vs.^ and E)

will still yield sufficiently accurate values for the absorption corrections.

3. Decay Curve Analysis : Interpretation of Statistical

Parameters

A computer program for the analysis of multicomponent decay

curves has been prepared in BASIC for use with the time-sharing

computer (See Section 2. A. 5). A detailed discussion of the

program, its use, interpretation, and examples are given in

Appendix I. The principal point to be made here is that by

careful examination of the statistical parameters which are

included in the output, one may frequently locate sources of

error either in the experimental data or in the model assumed.

67
The "on-line" aspect of the mathematical analysis leads to an

enormous advantage with respect to rapid changes in model or

data (where permissible) in response to such statistical indicators. Such changes, of course, must have valid physical and

statistical bases.

The principal indicators of possible systematic error include: results which are negative by more than a few times the

2 corresponding standard errors; x /v , as a measure of goodness

of fit; and the magnitudes and trends of the ratios of the

observed deviations of individual observations to their assumed

standard deviations. (Reasonable limits for these indicators

are tabulated in Appendix I.) Among the errors which may be

detected are: "wrong" observations (outliers), wrong "models"

(for example, missing components or incorrect half lives) and

extra sources of random error. This last aspect may be of

particular importance with respect to the standard error

estimates for the components. The on-line "trouble-shooting"

use of the program is illustrated in Appendix I, taking data

from radionuclide mixtures produced in photonuclear and

fission reactions.

4. Detection limits and the Planning of Experiments

An examination of the statistical aspects of radiation detection has been carried out for two purposes: (1) to specify

statistically-meaningful "limits of detection" for radioactive

species resulting from nuclear reactions, (2) to plan experiments in such a manner that an optimum or satisfactory detection

limit is achieved. Limit of detection is here taken to be that

level at which the relative standard error for the radioactivity

in question is equal to 0.50. This somewhat arbitrary criterion

results from a compromise between errors of the first and second

kinds. Specifically, it is equivalent to accepting about a 36%

probability of failing to detect a "real" sample where the test

is carried out at the 5% level of significance. It should be

recognized that the detection limit, which refers to a "true"

68
limiting activity level, is not the same as the critical level,

above which an observed result is considered significant.

In the absence of interfering radionuclides, the detection

limit, A , may be expressed as

A

m

" «T U + t 1 + V

1/2

> < 2)

where e represents the detection efficiency; T, the "mean"

counting interval; and N, , the number of background counts. , Equation (2) assumes that the background is well known, and it

applies equally well to long-lived species and to those which

decay significantly during measurement. Calculations based

upon the above equation have allowed the selection of "best"

counting systems for long- and short-lived radionuclides depending upon the relative efficiencies and backgrounds of the

various possible detectors. The form of equation (2) also

allows one to specify useful lower limits for the background

and its standard deviation.

For many detection systems there are continuously variable

parameters, such as upper and lower discriminators which alter

both the background, b, and detection efficiency, e . As a

result, in order to design the method of detection to give the

minimum value for A , it is necessary to express b and e in

terms of the continuous variables, and to analyze the system

by means of equation (2). Such an approach to a "triangular"

efficiency curve accompanied by a "rectangular" background

curve, for example, led to the conclusion that the minimum

detection limit obtains when the discriminator includes about

2/3 of the energy interval centered about the peak. The best

setting, however, does depend upon the value of N, , and the

above result applies only when N, »1.

When there are several radionuclides which must be observed simultaneously and resolved by means of decay analysis

or spectrometry, the effects of interference upon the respective detection limits must be considered. The particular

problem of decay curve analysis has been dealt with using a

69
suitable modification of the previously discussed computer

program. The calculation cannot be carried out directly but

requires an iterative procedure which is based on the general

form of equation (1) and the requirement that the relative

standard error of A be 0.50. In this way, one may determine,

a priori , the limit of detection for a given radionuclide in

a mixture having specified levels of other radionuclides.

On the basis of such a calculation, one may introduce

changes into the experimental plan (different irradiation and

delay times, counting intervals, detection systems, chemical

separations, etc.) so as to attain a more satisfactory detection limit, if desirable. In order to serve as an illustration,

a calculation has been carried out for a hypothetical experiment involving two nuclides: one considered the contaminating

activity having an 18-minute half life, and the other, the

activity of interest, having a 20-minute half life. Two observations were assumed: one starting at the end of irradiation

and one starting 31.5 minutes later. The first observation

had a time interval of one minute; the second observation, two

minutes. The detection limit for the 20-minute activity at

the end of the irradiation was calculated for three different

situations as shown in the following table.

Table 12. Detection Limits

18 minute 20 minute

contaminant initial activity

initial activity detection limit

interference-free Absent 9.8 cpm

interference cpm 740 cpm

interference 600 cpm 1080 cpm

A striking difference is seen between the interference -free

case and that case where the 18-minute activity must be determined from the data, even though its contribution is zero. The

difference is pronounced in the example, because the resolution

70
is difficult under the conditions of the hypothetical experiment. When such cases of "difficult" resolution arise, the

plan of the experiment may be suitably modified - for example,

by eliminating the 18-minute component or by determining it

with another type of detector. One point in presenting such an

extreme example is to indicate the significant effect of the

possibility of interference, per se, even though the contribution of the interfering nuclide may be negligible.

By way of summary, the iterative approach is being applied

to problems in activation analysis in order to (1) deduce detection limits for given procedures both in the presence and

absence of specific kinds of interference, and (2) to assist in

the design of the radiochemical and data-taking procedures in

order to arrive at acceptable limits of detection.

(L. A. Currie)

E. Radiochemical Separations

"Radiochemical Separation of Copper by Amalgam Exchange "

1. Introduction

The radiochemical separation technique by amalgam exchange

has been successfully developed for and applied to such elements

as Cd, In, Zn, Bi, Pb, Tl, Sr, and Hg [24 -321. Symbolically,

the process may be expressed as follows:

M»(Hg) + M^^/fHg) + M^

where >r(Hg) represents the metallic liquid amalgam and

M „ is the radioactive metallic ion dissolved in the aqueous

phase. These soluble amalgam systems have demonstrated high

exchange yields with accompanying good decontamination when

agitated with aqueous solutions of their respective radioactive

metal ion in the presence of many interfering elements. It is

desirable to expand this technique to other metals which possess

little solubility in mercury.

Copper, an element only sparingly soluble in mercury [ 33]

,

is often determined by activation analysis. Its high sensitivity

71
however, is sometimes difficult to obtain because of interfering

gamma-ray activity in the 0.5 MeV energy region. A convenient

64.

method of successfully decontaminating Cu from many elements

would be desirable. Existing methods such as precipitation,

ion-exchange, chromatography, or solvent extraction sometimes

are not too efficient, specific enough, or must be coupled for

best results [34]. Development of an amalgam exchange technique

for this problem would be useful.

A liquid copper-mercury phase may be formed through electrolytic deposition of copper into mercury. The resulting mercury

phase is composed primarily of a finely divided suspension of

copper in an extremely dilute solution of copper amalgam. Preliminary experiments revealed that appreciable isotopic exchange

readily occurred between the deposited copper in the mercury

phase and radioactive cupric ions in the dilute acid solution.

This was encouraging since previous investigators observed a

slow, unfavorable exchange between fine copper dust and an

aqueous solution [35].

In view of these results the system was investigated to

determine first whether the general requirements for a radiochemical separation technique could be met. These include high

overall yield, good decontamination, favorable reproducibility

and convenient time of separation. This necessitated development

of an optimized system derived from a careful study of all the

parameters involved.

In order to understand the underlying exchange process, a

kinetic study was undertaken. Parameters such as temperature,

concentration, and agitation conditions were varied to help

elucidate the mechanisms involved.

Finally, the evolved technique was tested for applicability

on standard reference materials by activation analysis.

2. Experimental

a. Optimization Experiments

(1) Preparation and Use of Amalgam. It was found

72
that the best isotopic exchange yields were obtained by amalgams prepared and used within a reasonable period of time.

For the preparation of a 1% copper amalgam, the electrolysis

was performed at 5 to 10 volts with currents from 0.5 to 3

amperes using little stirring. When excessive agitation was

employed (even under nitrogen atmosphere) the exchange yields

were significantly lower. Upon completion of electrodeposition

the amalgams were stored under distilled water and stirred i before each use. Amalgams stored for more than a day rendered

less quantitative results.

(2) Type of agitation . Various methods of intimate mixing of the amalgam phase with the aqueous solution were

attempted and evaluated for percent exchange and reproducibility.

Moderate shaking at room temperature was found to give only

10% to 20%, exchange in 5 minutes. A very high rate of agitation with a high speed shaker produced somewhat nonreproducible

(± 20%) yields of 20% to 30% in 2 minutes with the added undesirable properties of amalgam decomposition.

An ultrasonic approach was tried by immersing the container

of amalgam and solution in an ultrasonic bath (80 watt total

power). This approach gave higher (507o to 90%) yields with a

reproducibility of ± 4% in 5 to 30 minutes agitation in an

approximately 50 °C water bath. Another procedure involved

the use of an ultrasonic probe which was immersed into the

aqueous phase at elevated temperatures (50 to 90 °C) and the

system agitated severely at concentrated high power (75 watts).

Agitation times of 5 to 10 minutes gave yields of 80% to 95%

with moderate (± 2 - 3%) reproducibility; however, experimental

conditions such as probe position, volume, and immersion levels

were too critical for routine use.

Quantitative (>99%) and highly reproducible (<1%) yields

were obtained in 10 to 12 minutes through moderate stirring

9

(~5 x 10 r/min) of the system with nitrogen bubbling at

>95 °C. This last approach, which is easy to manipulate and

reproduce, was adopted for further study.

73
(3) Copper Concentration in Amalgam and Solution

Phase . The % isotopic exchange was observed as a function of

the copper concentration in the amalgam phase. A comparative

study performed using the ultrasonic probe mixing technique at

90 °C showed 74%, 93%, and 93% exchange for 4 ml of 0.1%, 1%,

and 27, amalgam using 5 minutes contact with a 20 ml aqueous

solution containing 0.4 mg Cu . A similar study done with a

10-minute agitation at 95 °C showed 93% and 99.6% exchange

++

for 0.1% and 1% amalgams interacting with 0.3 mg Cu in 20 ml

aqueous solution.

Under comparable 10-minute stirring conditions with 1%

amalgam at ^95 °C the total cupric ion amount was varied and

exchange yields of 99.67,, 99.67, and 94.97, were obtained for

0.32, 0.96, and 8.0 mg Cu , respectively.

These results indicate that conditions of > 1% amalgam and

<1 mg Cu should yield an optimized quantitative initial

exchange.

(4) Temperature and Time of Stirring . Employing

a volume of 20 ml 1 M H^SO, containing 0.3 mg Cu , and mixing

with 1% amalgam, the per cent exchange of 74%, 94% and 99.47,

were obtained for 2, 5, and 10 minutes, respectively, of stirring at ~95 °C. The effect of temperature was evaluated thoroughly in a kinetic study and the data are summarized in that

section.

(5) Post -exchange stripping of Copper from Copper - Amalgam. Since the radioactive amalgams , after having exchanged

with radioactive Cu solutions, gave nonreproducible and

unpredictable counting results, a convenient stripping procedure

was needed. A successful chemical procedure was developed which

involved quantitative dissolution of the copper from the amalgam by a concentrated HNOo-HCl mixture.

b. Optimized Procedure . A 1% amalgam is prepared by

electroplating 5 g dissolved CuSO, from ~ 75 ml 0.2 M H

2 S0, into

16 ml triple distilled mercury with an applied voltage greater

than 6 volts and only very moderate stirring (100-200 r/min)

.

74
The resulting amalgam is stored in distilled water. In a 125 ml

round bottom flask, four ml of the amalgam is agitated for 11

minutes by a fast rotation ( ~ 500 r/min) stirring rod with

20 ml 1 M H

2 S0/ solution containing less than 1 mg cupric ion.

The procedure is performed while bubbling nitrogen through the

aqueous phase and maintaining the whole apparatus at 95 to 100 °C

in a water bath. The aqueous phase is removed, the amalgam

washed with water, and then 30 ml of a 9 to 1 mixture of concentrated HC1 and HNO- is added. This system is stirred for

about 5 minutes after a dark green color appears in the aqueous

layer. This copper stripping solution is removed, 10 ml more

of the HC1-HNCL solution added and the system stirred again for

10 minutes. The second stripping solution is removed and the

amalgam washed with 5 to 10 ml of 50% HC1 solution. The two

copper stripping solutions and the HC1 wash solution are combined and diluted to a known volume. Suitable aliquots are

taken for counting the 0.511-MeV peak of Cu. The overall

procedure requires about 40 to 50 minutes.

The optimized procedure described above was evaluated for

overall yield and precision by performing replicate runs using

0.4 mg Cu ion. The decontamination ability was evaluated by

subjecting the optimized procedure to various radioactive elements (2 mg inactive carrier each) and measuring the amount of

carrier through the entire procedure. The effect of the presence of varying amounts of HC1, HNO- , and HC10, upon the per

cent yield was also evaluated. Similarly the effect of presence of macro amounts (~1 g) of some salts was evaluated for

the system.

c. Procedure for Standard Reference Materials * Standard reference materials magnesium-base alloy 171 and nickelchromium cast iron 82b were analyzed. Samples weighing from

0.2 to 0.4 g and copper standards were irradiated for one hour

11 -2 -1

in a thermal neutron flux of ~8 x 10 " n»cm s

' with copper

foil flux monitors. The copper metal standards were dissolved

75
in dilute HNO~, taken almost to dryness in order to destroy

excess acid, and then redissolved and diluted to a known volume

with 1 M H

2

S04

. After a 12-hour decay period the magnesium-base alloy was

dissolved in~20 ml 1 M H^SO, and then treated according to the

optimized amalgam exchange procedure. An aliquot of the standard was treated identically.

Similarly, after about 12 hours decay the nickel -chromium

cast iron samples were dissolved in 20 to 25 ml 1 M H9 S0A with

0.8 mg inactive Cu carrier added. This was done to prevent

any possible adsorption on the undissolved carbon residue. The

samples were digested for ~1 hour, ~ 40 mg Zn° added and dissolved, and then the filtered solution treated according to the

optimized amalgam procedure agitating for 15 minutes. The

copper standard (0.808 mg) was exchanged in the presence of

0.2 g of dissolved inactive cast iron in order to approximate

the sample conditions.

In all cases the radioactive copper stripped solutions were

diluted to 50.0 ml, and 10.0 ml aliquot s were taken for counting

on a 3 in x 3 in Nal scintillation detector with a 400-channel

analyzer, integrating the 0.511-MeV peak.

d. Mechanism and Kinetic Studies . In order to evaluate the influence of temperature upon reaction rate, temperatures of 1, 22, 49, 67 and 99 °C were employed and the percent

isotopic exchange observed as a function of time. Volumes of

++

45.0 ml 1 M H

2 S0, containing 2.0 mg Cu were agitated with 4 ml

1% amalgam bubbling nitrogen through the system. Moderate speed

glass rod stirring (~5 x 10 r/min) was used. One or two ml

aliquots were removed at various time intervals for measurement.

In order to evaluate the effect of change in concentration

of cupric ion in the aqueous phase the concentration was increased fourfold and the percent exchange observed versus time

at 67 °C.

76
In order to evaluate the change in concentration of copper

in the amalgam phase the concentration was decreased tenfold

and the percent exchange observed versus time at 67 °C.

In order to evaluate the influence of stirring rate, the

rate was approximately doubled using the conditions of 1%

amalgam and 2.0 mg Cu

++

at both 49 and 99 °C.

3. Results ( a. Evaluation of Technique for a Radiochemical Pro- cedure* The technique appears to approach quantitative yields

with good precision. These results and the values for decontamination from various metallic ions are shown in table 13 . Table 13. Separation of copper and contaminants

by amalgam exchange

b

Tracer

22Na

140TLa

54Mn

54Mn(C.F.)

65

59

Reduction potential

volts

Zn

Fe

60Co

113

122

Sn

Sb

64Cu

110mAg

Na

+

/Na° 5 - 2.71

La /La , - 2.52

Mn+2 /Mn°, - 1.18

Zn

+2 /Zn°, _ 0.76

Fe

+2

/Fe°, - 0.44

r«+2 / r O LO /CO j - 0.28

Sn+2 /Sn°, - 0.14

Sb+3

/Sb°, + 0.15

Cu+2 /Cu°, + 0.34

Ag

+

/Ag°, + 0.80

Separated

%

0.0001

0.001

0.0001

0.001

0.0001

0.0001

0.001

0.05

1.9

98.5 ± 0.9

31

a Inactive amount of carrier in each case was 2 mg except

for copper which was 0.4 mg. C.F. = carrier free.

Data taken from Latimer [36].

c Cu value is average of 5 runs. Error is standard

deviation. Others represent two determinations.

77
Decontamination of most elements above copper in the electromotive series appears excellent, whereas those elements near

copper or lower are poor.

The technique is fairly insensitive to H

2 SO, HC1, and

HCIO^ while HN0

3

is detrimental to good results. ' These data

are graphically illustrated in figure 18.

>1 M for HC1 and HC104

, >3 M for ^SO,, and >0.1 M HN0o not be present if >98% yields are desired.

Concentrations of

>3

100

1 1 1 1 1

HCIO4

H

2 S04

90

* HNO3 \

WITH

WITH

1 M H2 S04

80

IMH2 S04 —

70

b HCI

\ WITH

\ IMH2 S04

-

60

50 1 1

1 1 1

=> qn —

ACID MOLARITY

Figure 18. Effect of mineral acids upon isotopic exchange of

cupric ion with 1% copper amalgam

78
Table 14. Activation analysis results.

NBS cert. Std

value for Sample dev

Material Cu,% size, g Found, % Ave % %

0.0369 2.2 Cast Iron 82b a 0.038 0.1915 0.0362

0.2487 0.0375

Mg Base alloy 0.011 0.3722 0.0113

171 b 0#4U8 0#0102 0.0108 6.4 '

a Fe = 92.7%, Mn = 0.75, Si = 2.1, Ni = 1.2, Cr = 0.33,

C = 2.8, traces of V and Ti.

b Mg >95%, Al = 2.98, Zn = 1.05, Mn = 0.45, traces of

Si, Pb, Fe, and Ni.

One gram quantities of Mn , Co , and Sn salts added to

the system do not affect the initial isotopic exchange yield

of > 99%. One gram of AgNOo , however, caused extensive oxidation of the amalgam incapacitating the exchange. As expected,

those salts having the metallic ion high in the electromotive

series do not interfere, paralleling decontamination behavior.

b. Activation Analysis of Standard Reference Materials , The results from activation analysis of SRM nickel -chromium 82b

and SRM magnesium- base alloy 171 are shown in table 14. Some

of the error is due to the many steps involved in the overall

activation process itself.

c. Kinetic Studies . A summary of the kinetic data is

shown in table 15. Results obtained from comparable experimental conditions performed at five different temperatures yield

data which fit two first order reactions. As the temperature

increases both reaction rates increase markedly, such that at

99 °C only the slower step is experimentally observed. The

reaction rates are plotted in figure 19 versus reciprocal absolute temperature and reveal general Arrhenius behavior over the

temperature range. The energies of activation for the two

steps are 5.1 ± 0.9 and 6.5 ± 0.8 k calth /mole for 1 and 2,

respectively. 79
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temperature

The fourfold increase in cupric ion concentration does not

result in much significant difference in half- life for the observed isotopic exchange. Similarly the tenfold decrease in

percent amalgam yielded no significant difference in the observed half -life for the faster step; however, the system was

too sensitive to oxidation, making the slower step nondiscernible.

The increased stirring rate at a lower temperature (49 °C)

resulted in a single initial step with no evidence of the second

81
slower step. At 99 °C however, comparable results with the

slower stirring rate were obtained.

4. Discussion of Results

The data indicate that the procedure satisfies general requirements for a radiochemical separation technique. Combined

yield, decontamination, precision, and time requirements are

favorable for general applicability. The technique is insensitive to many chemical interferences. Experimental conditions

such as amalgam preparation, temperature, stirring, timing,

and removal of copper from the amalgam are easily reproduced.

The technique has been successfully applied to some practical samples. The results demonstrate good overall accuracy

and precision. The procedure has a certain amount of flexibility so that it may be adapted to many chemical situations.

Certainly the analysis of low ( < 10 ppm) copper containing

materials would benefit most since excellent decontamination

is possible for many materials.

The kinetic data support the possibility that two dependent

steps are occurring simultaneously and contributing to the

overall isotopic exchange process. The first might be visualized as the faster initial surface exchange process followed

by a second slower process of general diffusion to and from the

surface, replenishing the surface with fresh copper. The rate

of agitation definitely plays a major role in diminishing the

slower step. A third opposing oxidizing step may interfere

severely with the overall process if low-percent or improperly

prepared (or handled) amalgams are used.

5. Conclusion

It has been clearly demonstrated that a finely suspended

copper-copper amalgam system can be adapted to a successful

amalgam exchange technique for the radiochemical separation of

copper from a variety of materials.

(R. R. Ruch)

82
F. Consultation and Liaison Activities

1. Mr. Gilbert W. Smith has been responsible for all of

the liaison activities indicated in Section 1-A of

this report.

2. The following are the consultation and liaison activities of Dr. Lloyd A. Currie:

a. Member of a task group preparing a report on the

measurement of low-level radioactivity for

International Commission on Radiological Units

and Measurements.

b. Discussed the merits of various types of low-level

systems for {^-detection with Dr. Hayes, of the

Department of Agriculture (Agriculture Research

Center)

.

c. Discussed availability of isotope separators,

particularly some of French design, and also the

radiochemical aspects of planning for an underground, low-level laboratory with Mr. J. Callow

of the National Physical Laboratory of the United

Kingdom.

d. Consultation on various patent applications which

were related to radioactivity with Mr. H. Dixon,

Patent Attorney of the Atomic Energy Commission.

G. Publications

1. Becker, D. A., and Smith, G. W. , "Determination of

Trace Amounts of Tellurium in Standard Reference

Materials by Neutron-Activation Analysis," Proceedings

of the 1965 International Conference: Modern Trends

in Activation Analysis, Texas A & M Univ., College

Station, Texas.

2. DeVoe, J. R. , and Smith, G. W. , "Activation-Analysis

Program and Facilities at the National Bureau of Standards," Proceedings of the 1965 International Conference: Modern Trends in Activation Analysis, Texas A &

M Univ. , College Station, Texas.

83
3. INSTRUMENTATION

The efforts of the Instrumentation Group during the past

year have been directed toward the improved handling of data

gathered by automatic equipment. The completion of the interface project first described in a previous report [37] has been

completed along with the design and construction of a fast rise

preamplifier and the setting up of a solid state detector program. A high memory capacity pulse height analyzer, a TMC*

4096 channel system, was set up to be used with both the solid

state detectors as well as scintillation detectors. The analyzer is capable of two parameter storage in binary subgroups up

to a 64 x 64 channel array or a full 4096 channels for high

resolution singles spectra. The input-output system for the

4096 channel analyzer incorporates a high speed line printer

and computer -compatible magnetic tape unit.

A. Interface Units - Final Report

1. Interface Translator Units

Six of these units have been built which provide readin and

readout capability for each of the multichannel analyzers in

use by the Radiochemical and Activation Analysis Sections.

The interface units are completely described in a paper

presented at the 1965 Activation Analysis Conference, College

Station, Texas [38] and are discussed here briefly through

excerpts from the paper with the final schematics including

all subsequent changes and improvements.

The system is comprised of three parts: phase I (figure 20)

is the interface translator unit providing the readout function,

phase II (figure 21) is the readin section allowing data previously read out on punch tape to be reintroduced into an analyzer's memory, and phase III (figure 22) is the precursor data

section which provides time of year, identification, and other

externally gathered data to be formated ahead of the analyzer's

For disclaimer of equipment and materials see last paragraph

of preface.

84
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»*-

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Oyo" • I a: o X CNCM

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bO

•r-( fe

<k h (k ® M^k b A <4 <£> 1 f..i.i

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87
normal read out. System control is also provided by the circuit

(figure 23). The interface units were built of modular circuit

boards designed by the Data Automation Group of the National

Bureau of Standards. [39]

2. " Basic" Format Units

Three of the interface units have been modified for special

application for use with a multistation input computer which is

programmed to accept data in the "BASIC" format. The format requires that each line of data be preceded by a line number and

then the word "DATA." The serial converter board of the analy*

zer was reprogrammed such that only the first two digits of the

address were scanned, then followed by four preprogrammed digits

representing the BCD form of the word "DATA." Two additional

leads were brought out from the serial converter board to provide the logic levels necessary for the interface to complete

the code structure.

3. Adaptors for Interface Unit s In order to use the interface units when an analyzer was

coupled to a high speed magnetic tape system, it was necessary

to introduce a switch-over box between the units. The modes of

operation permitted are: teletype, readin and readout, magnetic

tape record and playback and magnetic tape playback with teletype readout. This last function enables an operator to automatically print hard copy or punch tape of a series of spectra

automatically accumulated on magnetic tape. Another switchover

box similar in design was built to be used with the RIDL 34-26

"Nanolyzer"* thin film memory analyzer which eliminates the

necessity for modification of the standard interface design.

4. The RIDL Model 34-27 Analyzer* The RIDL Model 34-27 Analyzer can be used with the unmodified interface unit but requires some program changes and

modification to the serial connector board in the analyzer.

For disclaimer of equipment and materials see last paragraph

of preface.

88
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89
5. Reliability

The reliability of the interface units has on the whole

been satisfactory. During the past year, however, several

deficiencies have been noted and design changes made (See

figures 20, 21, 22) notably, revision of the "interlock circuit" in phase I, the "bit transfer gates and monostables"

in phase II, and the "precursor start up" phase III.

(R. W. Shideler)

B. Time of Year (TOY) System

1. Time of Year Clock

To provide time of year information to the interfaceanalyzer data readout system, a long term clock had to be

obtained. Of the clocks known to be available commercially

which are capable of electronic readout with sufficient resolution most had drawbacks. Decimal days were judged to be an

inconvenient time form and electronic scalers had a tendency

to fail to change state in the digits that remained unchanged

for long periods. Also all of the clocks available were very

expensive. A new design was made in order to overcome these

deficiencies.

The design centers around an electromechanical digit

counter having individual contacts for electrical readout and

capable of very fast reset. Eight of these counters provide

999 days, 23 hours, and 59.9 minutes. A synchronous motor

with a cam-operated switch provides impulses at six seconds

(0.1 min) intervals driving the least significant digit

(figure 24). Each digit provides a carry after the nine and

relay logic performs the resets at 60 minutes and 24 hours.

Provision is made to set the clock to any permitted state and

a warning light and circuit shut off the clock in the event

of a power failure. Provisions were made in the clock to

allow time manipulations as described below. An anticipated

addition will increase the readout resolution to 0.01 minutes.

90
^TM

el @l ®l ®|

91
2. Time of Year (TOY) Clock Controller

Complete timing information for a given spectrum is only

obtained if one knows the start time, the stop time, and the

live time of the analyzer taken during the run. It is therefore necessary to synchronize either the clock with the analyzer or vice versa. A control circuit (figure 25) was designed

which sets the clock ahead 0.1 minute when the analyzer is

manually set to store and prints this time only while holding

the analyzer from storing. When the time pulse corresponding

to the clock reading occurs, the analyzer is started synchronously while the clock resumes normal timing. At the end of

the store cycle the analyzer automatically starts the readout

cycle. The clock is stopped and held until the time has been

read out and then restarted catching up by one time pulse if

necessary. The logic for these operations is performed by a

system of relays and contained in the clock chassis.

(R. W. Shideler)

C. Time Mode Control Unit

In multichannel scaling using the RIDL Model 34-12* series

analyzer it is necessary to provide an external timing source

to advance the address scaler. A convenient means for generating this signal is available in the analyzer by making use

of the built in clock if the desired channel advance rates

are not too high. A simple circuit (figure 26) has been designed for use with units not having built in** or auxiliary

timers available. An additional mode of operation is included

which allows the experimenter to start each time interval on

an individual or channel -by -channel basis,

(R. W. Shideler)

For disclaimer of equipment and materials see last paragraph

of preface.

Available as standard option by manufacturer.

92
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93
MULTISCALER CONTROL

DETECTOR

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16 n + 10

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INPUT Figure 26. Time mode control unit

94
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TIMER.

p«r/> zines

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Figure 27. Data logging system (block diagram)

D. Data Logging System

A system comprising three scalers and a timer was assembled

using an electric typewriter and relay driver formerly used as

an analyzer readout. An interface unit (figure 27) was designed using modular circuit boards [39] although some modifications were required. The circuit provides 31 readout

locations and resets automatically after printing.

(F. C. Ruegg and P. N. Thomas)

E. Fast Rise Preamplifier

For achieving meaningful results in very fast ^20 ns coincidence work, a preamplifier must have rise times at least

as fast as the time resolution of the coincidence experiment.

A preamp was designed utilizing the properties of the relatively unpopular and unexplored current mode input (figure 28).

The input stage (TI) base is grounded while the signal is introduced on the emitter which is directly coupled to the current

signal source as well as to a stabilizing feedback bias. The

95
®—<\

-6V

Figure 28. Fast rise preamplifier for current signals

input impedance in this mode is less than 50 p . The transistor

is operated at very low collector current to achieve low noise

operation. This stage is followed by a double "Darlington"

circuit made up of two complementary pairs of transistors (T2

through Tj in a direct coupled self -compensating circuit.

The output is an emitter follower transformer coupled to match

a 50 n cable impedance. Exclusive of the transformer the D.C.

current gain is on the order of 100 while with 20 ns pulses a

current sensitivity of 200 /zA/volt into a 50 n load is realized.

The preamplifier was designed for fast rise characteristics

only and its gain and therefore linearity are dependent on

input wave shape. Further work will be done to remove restrictions arising from wave shape dependency and broaden its

utilization.

(R. W. Shideler and J. J. Spijkerman)

96
F. Solid-State Detector Systems

In the last few years gamma-ray spectrometry has been provided a new and most powerful tool in the cooled solid-state

detector. In line with this fact a system has been set up to

make these potentialities available to the activation analysis

group as well as for other research. Although the germanium,

lithium-drifted detectors are far superior in performance at

high energies to silicon lithium drifted detectors, the silicon detectors are far more rugged and can be used at room

temperature as particle detectors. These facts have caused us

2

to divide our attention making use of a 300 mm x 5 mm silicon

lithium-drifted detector for low and medium energy (20 to 200

2 keV) work with a 100 mm x 3 mm deep germanium lithium-drifted

detector for higher energies. A second silicon lithium2 drifted detector 60 mm x 2 mm deep is being set up with a

10-mil beryllium window for very low energy X-ray work.

G. Observations on Calibration of a Pulse Height Analyzer

Using a Sodium Iodide Detector

In a laboratory doing activation analysis where sodium

iodide detectors are used to provide gamma-ray spectra of many

various radioactive species, instrument calibration can present

a problem. This is especially true if the experimenter wants

only a quick look at a sample during or before further preparation. In this instance, unless the peaks obtained are close

to the calibration points or are quickly recognized, an energy

determination and isotope recognition becomes an arduous task

or an idle speculation. This is due largely to nonlinearities

(as much as 10 to 15%) inherently present in the sodium iodide

detection mechanism shown by Engelkemeir [40]. Ordinarily,

initial calibration for nonspecific or routine pulse height

analysis is done in one of two ways. Either the photopeak of

137

Cs is used to establish 0.662 MeV on the energy scale with

137

a zero intercept end point or the Cs photopeak is used in

conjunction with its associated Ba K X-ray to establish a lower

97
point at 32 keV. These calibration methods along with an improved technique are depicted graphically, figure 29, and

include the position of several familiar photopeaks showing the

Engelkemeir nonlinearities. The abscissa is the energy of the

detected gamma ray with the ordinate being Pulse

Energy

UnltS

and normalized to the Cs photopeak. A one-point calibration

137 normalized to the Cs photopeak and zero intercept (figure 29a)

shows large errors over the entire range. A two-point calibra137 tion normalized to both peaks of a Cs source (figure 29b) is

an improvement but has significant errors throughout most of

the spectral range peaking between 60 and 85 keV at about 10%.

The third graph (figure 29c) was normalized using the 60 keV

o/i

photopeak of Am as a convenient lower calibration point with

a general improvement in rudimentary energy determinations over

the most frequently used energy range with an error of no more

than +6% at 85 keV and -4% at 3 MeV. Below 32 keV where there

is an error of -15% the error becomes quite serious but this

region is rarely used in routine work and never without careful

calibration.

The above considerations clearly indicate the desirability

of a two-source calibration using Cs and Am. Another

137 technique, equally suitable, is to use Cs and the BaK X-ray,

but to consider the BaK X-ray not as 32 keV but instead 15%

lower or approximately 27 keV. This approach produces equivalent results to that of using two separate sources.

H. Pneumatic Transport System Rabbit Sensor

In performing activation analysis and other precision

irradiations it is often necessary to determine exactly the

arrival and departure time of a rabbit or sample carrier to a

high flux location. The high fluxes present in such a location make the problem difficult inasmuch as no known electrical

device can survive in such a hostile environment for a time

long enough to be practical. It is customary in such situations to measure the time as the rabbit goes past some point

98
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1007,

>-o

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UJ

1007,

TRUE ENERGY IN M«V

.060J085 0.150 O340 0662 1.33 2.90

B TWO POINT CALIBRATION

110—

|

100% &%%>>*+. r+^4£^

C IMPROVEO TWO POINT CALIBRATION

NORMAL RANGE —

CROSS HATCHED AREA= ERROR

Figure 29. Calibration methods used with sodium iodide

detectors

99
remote from the irradiation area and knowing the rate of travel

extrapolate to determine the true time.

A new approach has been suggested and preliminary tests

have been made on a system to alleviate this problem. The system is to make use of a principle known as pneumatic gaging.

The end bumper for the rabbit is shaped to conform to the shape

of the rabbit and contains a small orifice axially located

which connects to a small bore tube that returns to an environmentally safe location. At this point, a fast response pressure transducer or switch and a source of high pressure gas

(CCO is connected through a constant flow regulator which

completes the system (figure 30).

In operation the system pressure at the pressure sensor is

established as a dynamic equilibrium between the pressure drop

across the constant flow regulator and the relatively small

pressure drop due to the small bore tubing and the orifice.

When the rabbit comes near to, or in contact with the orifice,

the flow rate at the orifice drops dramatically causing the

pressure at the sensor to rise sharply providing contact information. This sensing system is being incorporated in the

pneumatic tube irradiation locations at the NBS reactor.

I. Consultation

In the past year, occasional consultation has been performed for persons or groups outside the section. Most notable

was work done for Dr. Kurt Heinrich of the Spectrochemical

Analysis Section in connection with adaptation of a 1600-

channel analyzer to more appropriately serve his specialized

requirements for the electron microprobe.

(R. W. Shideler)

100
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101
4. RADIATION TECHNIQUES

MBssbauer Spectroscopy

A. Introduction

The continued increase in MBssbauer Spectroscopy research in

the United States and abroad, and the applications in physics,

chemistry, metallurgy and biology has encouraged the NBS group

to continue their effort in instrumentation and standardization.

The first Standard Reference Material for MBssbauer spectroscopy,

SRM 725^ (sodium nitroprusside) has been certified [41] and is

available from the Office of Standard Reference Materials. Figure

31 shows the certificate accompanying each of these standards.

The NBS MBssbauer spectrometer has been further improved by the

addition of a multiplex unit to obtain true spectra simultaneously for comparison or for direct calibration against the standard.

Further efforts were made in the interpretation of the chemical

shift, by recalibration of the Walker, Wertheim and Jaccarino [42]

diagram with the standard and correlation with molecular orbital

calculation results.

The research in MBssbauer sources has been continued through

a careful analysis of the Pd-Sn system [43]. The Pd~Sn inter

11 Qm metallic compound exhibited better characteristics for a Sn

source and a high specific activity source can be obtained.

In the last fiscal year 85 persons visited the MBssbauer laboratory, and approximately 14 hours a week were devoted to consultation with 60% U. S. Government agencies and 40% outside.

(J. J. Spijkerman)

B. Facilities

The relocation of the Radiochemical Analysis Section from the

Washington laboratories to the new Gaithersburg site has made

possible a considerable expansion of the MBssbauer spectroscopy

program. The available space has been divided into a source preparation laboratory, absorber preparation and hot atom research

laboratory and a measurement laboratory. The proximity to the

NBS reactor, linear accelerator and the Activation Analysis Section neutron generator considerably extends the potential of the

MBssbauer spectroscopy group in the area of new MBssbauer isotopes

and sources.

102
U. S. Departn^^ of Commerce

John T. Coryj^c, Secretary

Standards

^Director (Utttxixtutt tti (ttalthraium

Standard Reference Material 725

for

Mossbauer Differential Chemical Shift for Iron-57

Disodium Pentacyanonitrosoferrate Dihydrate

(Sodium Nitroprusside)

This Standard Reference Material was prepared from a single crystal of the compound disodium penta- cyanonitrosoferrate dihydrate (Na2 Fe(CN) 6 N0.2H2 0). The purity of this compound, also known as sodium

nitroprusside, meets the specifications of the American Chemical Society for reagent-grade materials as

verified by quantitative analysis of the main constituents, but should not be considered as entirely free from

impurities such as heavy metals. It is in the form of a platelet of dimensions 1x1x0.0775 ±0.003 cm that has been cut from a large single crystal. The lxl cm surface is parallel to the 100 crystal plane within —1

degrees of arc. The opposite lxl cm surfaces are parallel to within 0.001 cm with a surface finish of 20

microns. The natural iron concentration is 25.0 ±4 percent mg/cm2

. The chemical shift of this Standard is compared to that of the National Bureau of Standards Primary

Standard, consisting of the average chemical shift of ten platelets which is given the value of zero chemical

shift. The National Bureau of Standards dual-spectra Mossbauer spectrometer [1, 2] was used. This Standard has an average value for the chemical shift of 0.0000 ±0.0002 cm/s at 25.0°C. This uncertainty is ex- pressed as the standard deviation of a single determination derived from single measurements on 50 platelets. The resonant spectra have considerable line-broadening due to the thickness of the absorber. The

experimental line width (full width at half maximum) is 0.0305 ±0.0004 cm/s. The line width corrected for thickness broadening is 0.0202 cm/s. The Mossbauer effect is 17 percent. To allow the user to calibrate the velocity scale of a Mossbauer spectrometer, the electric quadrupole

splitting of the Standard Reference Material was measured. The velocity scale of the dual-spectra comparison spectrometer was calibrated by measurement of the electric quadrupole splitting of the Primary Standards using an optical interferometric technique. The average value of the electric quadrupole splitting for

this Standard is 0.1726 ±0.0002 cm/s at 25.0 °C where the uncertainty is expressed as the standard deviation

of a single determination derived from single measurements on 10 platelets. The details of the instrumentation and of preparation and measurement of the sodium nitroprusside

crystals are given in NBS Miscellaneous Publication 260-13 entitled "Mossbauer Spectroscopy Standard

for Chemical Shift of Iron Compounds." The single crystal platelets of sodium nitroprusside were prepared by the Isomet Corporation of Pali- sades Park, New Jersey. The calibrations of the crystals were made within the National Bureau of Standards Institute for Materials Research, by J. J. Spijkerman, F. C. Ruegg, D. K. Snediker, and W. L. O'Neal

of the Radiochemical Analysis Section, James R. DeVoe, Chief.

References:

[1] Radiochemical Analysis: Activation Analysis, Instrumentation Radiation Techniques, and Radioiso- tope Techniques, July 1963 to June 1964, James R. DeVoe, Editor, NBS Tech. Note 248, pp 25-37 (1964). Available from Superintendent of Documents, Government Printing Office, Washington, D. C. 20402, 50 cents a copy.

[2] Radiochemical Analysis: Activation Analysis, Instrumentation, Radiation Techniques, and Radioiso- topes Techniques, July 1964 to June 1965., James R. DeVoe, Editor, NBS Tech. Note 276, pp 74-110 (1966). Available from Superintendent of Documents, Government Printing Office, Washington, D. C. 20402, $1.00 a

copy.

Washington, D. C. W. Wayne Meinke, Chief

April 6, 1966 Office of Standard Reference Materials

(over) Figure 31. Certificate of calibration for Mossbauer Standard

dated April 6, 1966

103
Directions for Use

The Standard Reference Material in the form of a single crystal platelet is sandwiched between two

pieces of a 4 mil polyethylene film. Due to the advisability of keeping it free from moisture it is recom- mended that the platelet not be removed from this container. A suitable mounting consists of two concentric aluminum rings approximately 1.25 inches in diameter. The crystal, encased in the plastic envelope,

is placed between the rings and the assembly is fastened together with small screws, thereby clamping the envelope firmly between the rings. Both rings have an inside diameter of 0.75 inch to expose the crystal and

to prevent crushing of its edges. This was the procedure used in taking all of the data at NBS on this Standard Reference Material. Place the Standard Reference Material as the absorber at 25.0° C in the Mossbauer spectrometer and

take sufficient transmitted counts of the 14.4 kev gamma-ray from an iron-57 source to obtain counting

statistics to the required degree of uncertainty. Determine the peak position of the electric quadrupole

splitting. The use of digital computation techniques are recommended. Divide the distance between the peaks by two and assign this as the value for chemical shift indicated above. Replace the Standard crystal with the compound whose chemical shift is to be measured as the absorber in the spectrometer. Measure

the peak position parameters as a difference between that of the unknown compound and the mid-point be- tween the peaks of the Standard.

104
The equipping of the source preparation laboratory is still

in progress. When completed this laboratory will contain a

10 kW induction furnace and a 10 kW electron beam evaporator

which may be used in conjunction with a high vacuum evaporating

unit. This apparatus is described in detail elsewhere [1, p 7].

The equipment in the source preparation laboratory, all of which

may be used with radioactive materials, makes possible a wide

range of functions in the preparation and purification of

sources, the study of thin film and surface phenomena and the

preparation of ultra-thin calibration absorbers.

The absorber preparation and hot atom research laboratory

is a conventional radiochemical laboratory containing two

radiochemical fume hoods and a glass vacuum line. A portion

of this laboratory is shown in figure 32. These facilities

allow the preparation of various compounds as may be required

Figure 32. Radiochemical fume hoods and

glass vacuum line

105
by the Mossbauer spectroscopist for use as absorbers or sources.

In addition the laboratory -will be used in conjunction with the

expanding hot atom research program of the Radiochemical Analysis Section.

The measurement laboratory is equipped with two constant

acceleration MOssbauer spectrometers [1, p 89] [44] each capable

of multiplex operation as described elsewhere in this report

and a high precision constant velocity spectrometer [1, p 84].

The electronics associated with the two constant acceleration

spectrometers have been integrated into a single console shown

in figure 33. Supplementary to the new multiplex units, the

Figure 33. Control console for constant acceleration

spectrometer

106
* 2

Figure 34. Helium cryostat

electronics have been expanded by the addition of a binary

overflow scaler which determines the number of times a spectrum

has overflowed the memory of the analyzer. The low temperature

research capabilities have been expanded by the addition of a

50 liter helium Dewar to the 5 liter research cryostat (figure 34)

In addition, a teletypewriter computer station to two area

computers is available. All spectra are recorded on paper tape

and sent to the larger of the two computers via the teletypewriter for analysis using the program described elsewhere in

this report. The smaller computer is extensively utilized for

associated computations.

(D. K. Snediker)

107
C. Computer Program for Curve Fitting of MQssbauer Spectra

1. Introduction

A computer program based on an iterative least square fit

has been written to process MOssbauer spectra. The program

was designed to be used on a CDC 3600 computer, but can be

easily modified to be used on a comparable computer with a

Fortran IV compiler and double precision arithmetic. A curve

plotting routine is also added to provide visual as well as

numerical output of the analyzed spectra.

2. Iterative Least Squares Fit to an Arbitrary Number of

Lorentzian shapes Superimposed on a Parabola

We assume the MOssbauer spectrum can be fitted to

y

= £jl+Btk-C>) 2

}

+F^x+Hx2

(1)

where x i s the energy scale and n is the number of Lorentzian

shapes with peaks at CI, heights A f

. , and half-widths at halfmaximum 1/B f

. . We now assume [5]

J C f

. - C . + y . where C . » y . (2)

and B

T

. = B. + B. where B.»6.. (3)

Keeping only first order terms in y . and B '.

,

A. 1 y~I>-

VX + B^x-C^ 2

+ BjCx-C^ 2

- 2y

j

B

j

(x-C

j

) )

+ F + Gx + Hx2

(4)

Expanding equation 4 in a Taylor series about B = y = to

first order, we have

D.(x-C) E.(x-C) 2

}

[l+BjCx-Cj) 2

]

2 [l+B^x-Cj) 2

]

2

)

+ F + Gx + Hx2

(5)

108
where D. = lA.y.B. and E = -A -jPn*

Defining Pj. = ^-C. and q

±

. = 1 + B.(x-C.) 2

, J J *J J J

(6,7)

(8,9)

we now require that

S

=

2 _

1 ^-^ ( r A. D.P. . E.PZ

, , Z wi u -e [e - -41 - -^ - F - Gx

i

- :

(10)

i\

be a minimum, in order to obtain a least squares fit. In

equation 10 the subscript i refers to the experimental data

points or channel numbers and the w. are arbitrary statistical

weights which may be attached to the data if so desired. (In

the current computer program, all data are equally weighted,

that is, w. = 1).

The constraints -rr~

3

bs __ ds __ ds _ o^s _ o^s _ c)s _ 3D" 3E7

j

W ' 3g~ M

yield 3n + 3

=

(11)

linear equations in the 3n + 3 unknown fit parameters A., D .

,

E., F, G, and H. From ds/^A-i c 0, we have n equations of the

J form

£

w.

IAJ

i <kj ail

+ dj?

wiPii

+ E

i q ij^ii

iZ

wjpV

i <* ij^ii J

Z^qtl

i

+ G E

wix

i

<ki

.w.x + "Sill -Sw_£i

ill

ds _

(12)

The n equations obtained from ^ = are of the same form as

equation 12, except that each term in the sums over i must be

multiplied by P-ji/cUi « The n equations from ds/ dE/ = may be obtained from those for a 3s/ dIV = by multiplying

in g, each term in the sums over i by P.,. From "ds/bF = we

have an equation which may be obtained from equation 12 by

109
deleting q,, . The equation from ds/dG = can be derived from

that for £s/ dF = by multiplying each term in the sums over

i by x,. The equation from ds/ dH = can then be obtained

from that for ds/dG =^0 by again multiplying each term in the

sums over i by x.

.

The above 3n + 3 linear equations may then be solved for A .

,

D., E., F, G, and H. (Computation time may be saved by noting

that the coefficients of the unknown fit parameters in a least

squares fit form a symmetric matrix) . From A . , D . , and E . , p

.

and y. may be obtained from equations 6 and 7 above* Inserting

these values into equations 2 and 3, one may replace C. and B.

in the above 3n + 3 equations by CI and B T. and again solve for

the fit parameters. This iteration may be continued until desired accuracy is obtained, according to various convergence

criteria. (In the current computer program, percentage difference convergence criteria are applied to A., B., and C.)«

Our linearization of equation 1 in the fit parameters B f

. and CI to a first order approximation thus leads to an iterative

least squares fit which will converge to a least squares fit of

the data for equation 1 itself, provided the initial estimates

of the Lorentzian peak locations and widths are sufficiently

close to the most probable locations and widths, assuming equation 1 is capable of giving a sufficiently good fit to the data.

In practice, convergence is insensitive enough to the initial

estimates, so that the desired accuracy is obtained in only a

few iterations, according to our convergence criteria. We know

of no simple transformation of equation 1 into one exactly

linear in all of the parameters.

3. Error Calculations

For the error calculation it is sufficient to obtain the

variance of the fitting parameters. Since the amplitude varies

linearly, the variance can be obtained from

S.A." 1

VAR (A.) = —f-

(13)

A'

3

110
where „

2 2 dev^

S

2

«

1

k-N

with N the number of coefficients to be fitted, and k the number of data points (channels)*

In the least squares fitting technique by iterations, the

peak parameters are not calculated, only their corrections. The

error in the corrections will therefore equal the error in the

final parameter value. Since the correction computed for the

halfwidth is D., (equation 6), the variance of the halfwidth is

4i f^ S^ S-A 1H1

2 a A 2 var(h.) - -51 rrr1 + -r21 + m < 14 >

Similarly for the peak position

A?. S«A. S'A^. S.A.,5.

VAR(P.) « —ii- -—L+-PJ. + ILL. ( 15 )

J 2H.A. A. A*. A. -A,,.

J J J p J J Pj

The standard deviation is now defined by the square root of

the variance.

4. Computer program

The computer calculations are made using equations 10, 13,

and 15. A flow diagram is shown in figure 35, and the loading

of the instructions, identification and data in figure 36. The

complete program is listed in Appendix II. The program is

written for a Control Data Corporation 3600 computer in Fortran

5.1, with a plot package for the Calcomp plotter. The fitted

spectra of a single crystal of Na«Fe(CN) ,-NO 'HIJO and that of

a commercially obtained enriched iron foil are shown in figures

37 and 38.

Ill
Conclusion

The program has been of great value in MBssbauer spectroscopy, particularly in resolving complex spectra. For doublet

type spectra, computer running time is approximately 10 seconds

per spectrum while for 9 line spectra about 1 minute is required.

58

99

101

112

114

124

126

167

J69

390

460

690

695

780

READ

1. INSTRUCTIONS

2. IDENTIFICATION

3. DATA

ZERO TEST

BEGIN, END

IGNORED CHAN

MAXIMUM

ADD COUNT

OVERFLOW

PRINT IDENT.

NORMALIZE

PRELIMINARY CALCULATIONS

FILL LEAST SQUARE

MATRIX

SOLVE

LEAST SQUARE

MATRIX

CORRECT

1. PEAK LOC.

2. PEAK WIDTH

60

1700

165

170

1600

/\.

805

843

844

966

967

981

984

993

994

1082

1084

1170

TEST

# ITERATIONS

CONVERGENCE

PUNCH

FINAL PEAK

PARAMETERS

PRINT

FIT 8. DATA

FOR EACH CHAN.

FIND MAX.

PLOT

NORMALIZED

FIT 8. DATA

DRAW 8. TIK AXIS NUMBER & LABEL

PLOT

IDENTIFICATION & LEGEND

1600+ i

1171^w>—»,

1205

1300

1310

INVERT

FINAL LEAST

SQUARE MATRIX

FIND COVARIANCES

J\

1470

151560

CALCULATE

STD. DEV.

1565

PRINT PARAMETERS

8. STD. DEV.

1700

1900

REWIND TAPES

END

Figure 35. Flow diagram of computer program for

curve fitting of Mossbauer spectra

112
The cost per spectrum including plotting averages about $8.00

per spectrum. Manual processing would cost approximately the

same (4 man-hours) but the precision would be a factor of 10

lower, and an error analyses would not be possible. Two peaks

separated by more than one half linewidth can be resolved.

The present program assumes Lorentzian line shapes, which

is not valid for spectra with broad lines such as encountered

3+

"

' in high spin Fe compounds. Other mathematical models are

being considered to more closely approximate the line shapes

predicted by Mdssbauer theories, including thickness broadening

and relaxation phenomena.

(E. Rhodes, W. O'Neal, and J. J. Spijkerman)

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20 CARDS- DATA

200 CHANNELS

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IDENTIFICATION

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PROGRAM

INSTRUCTIONS

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Figure 36. Loading instructions for computer program

Figure 36. Loading instructions for computer program

113
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115
D. Instrumentation

1. Cell for Producing Powdered Mftssbauer Absorbers of

Reproducible Thickness

The analytical applications of MBssbauer spectroscopy require a means of producing a powdered absorber of known reproducible thickness. The beryllium-window powder cell described

here provides the analytical chemist with an easily-used means

of producing powdered absorbers of known thickness without

resorting to a pellet press.

Figure 39 shows a cross-sectional view of the powder cell

assembly. In general the cell consists of a thick aluminum

disk (c) to which a fixed 10 mil beryllium bottom window (b)

is fixed with a clamping ring (d) . The removable 10 mil beryllium top window (b) is retained by a shim ring (a) . The thickness of the center portion of this shim ring determines the cell

thickness when a powder is placed in the volume between the

windows. Table 16 shows the relationship between the shim

thickness in inches (dimension x in figure 39 ) and the corresponding cell thickness in mm. These dimensions are valid only

if 10 mil windows are used. The cell is designed such that it

T"

1/16'

I I

r1/8' 1.

1/16

X

1/2

3/4

1-3/8

II lo

Figure 39. Cross sectional view of powder cell assembly

116
Table 16. Relationship between shim thickness

and cell thickness

x (in) 0.093 8 0.0544 0.0150 1 — — ^mm) l 2 3

may be loaded without removing the bottom window and clamping

ring. Uith these pieces in place the assembly is a convenient

container into which is weighed the absorber powder.

Figure 40 shows a spectrum of Sn02 in the powder cell with

a 1 mm cell thickness. The spectrum is identical in every

respect to the SnO« spectra obtained using other commonly used

absorber mounting methods. Although figure 40 represents a

spectrum obtained using a moving source geometry, the aluminum

cell is sulficiently light to allow a moving absorber geometry.

The latter geometry is mandatory in the case of iron-bearing

absorbers because of the interference resulting from trace iron

impurities in the beryllium windows.

2. Fast Response Controlled Atmosphere Furnace

The synthesis of the various tin-119-palladium iiossbauer

sources now in use [43, 45] requires a furnace with characteristics not found in common muffle-type furnaces. These characteristics are: extremely fast temperature response and controlled-atmosphere capabilities. In the synthesis of a tinpalladium alloy, it is necessary to melt p-tin ( b ^ = 2270 °o)

together with palladium foil (m.p. = 1552 °C). In order to

minimize the evaporation of tin during the melting process the

temperature of the crucible must be raised to ~ 1600 °C as

rapidly as possible. Furthermore, the heating should be carried

out in an inert atmosphere such as Ar or N„ in order to minimize

the oxidation of tin during the melting process. In general,

furnaces meeting the se specifications such as induction furnaces or self-contained vacuum systems are prohibitively

expensive for occasional source making.

117
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118
Figure 41. Phantom view of furnace

An inexpensive furnace has been designed and constructed at

the National Bureau of Standards which has the requisite charac1 1 A

teristics for mSn-Pd source synthesis. In principle, the

furnace is similar to self-contained vacuum systems in that the

crucible is surrounded by a tungsten basket that is connected

to two feed-throughs. The crucible-basket assembly is contained in a bell jar and is heated by passing current from a

high current power supply through the basket. Figure 41 shows

a phantom view of the furnace. All dimensions are approximate.

The base-plate (a) of the furnace is made from 1/2" thick

stainless steel. The surface is ground flat such that the Viton

gasket will seat properly. Stainless steel is used for the

plate because of its corrosion resistance and its relatively

low heat transfer properties. The base-plate is supported by

1/4" thick aluminum side plates (b) . These plates are in a

box configuration in order to provide a stable platform for

the heavy base plate.

119
The vacuum and gas flow system is constructed from 1/4"

O.D. copper tubing and torque-free swaged tube fittings. The

valves (c) are forged-body needle valves. The vacuum branch

of the system is designed to allow the evacuation of the bell

jar using a conventional positive-displacement pump. In addition to allowing operation as a vacuum furnace, the vacuum

capability speeds the purging of the furnace for inert gas

operation. The gas-flow branch is designed to allow the

connection of two different gas cylinders to the system.

Mixing can be done in this branch if desired. After passing

through the bell jar the gases are conducted through a flow

meter before being exhausted to the atmosphere in a radiochemical hood. A gauge (d) reading both vacuum and pressure

is fitted to the manifold at a location common to both the

vacuum and gas -flow branches.

The electrical connections to the tungsten basket (e) are

made through a pair of l/2 n O.D. copper high current feedthroughs (f ) . The feed-throughs are attached to the bottom

of the base plate with high vacuum flanges. Half-inch diameter

copper caps (g) are used to clamp the tungsten basket to the

tops of the feed-throughs. Current is provided by a 5 kVA power

supply. The specific voltage and current requirements depend

upon the type and size of tungsten heating element chosen.

For reasons of economy an inverted 15 cm vacuum desiccator

bottom is used as a bell jar. A vacuum seal between the

desiccator and the base plate is effected using a Viton gasket.

This arrangement has proven quite satisfactory in nearly all

respects. However, due to the relatively modest depth of the

desiccator, the desiccator bottom is quite close to the tungsten coil and has a tendency to overheat. This characteristic

limits the full power operation of the furnace to less than

five minutes.

This inexpensive resistance furnace has all of the requisite performance characteristics for the synthesis of tinpalladium MBssbauer sources. Heating rates up to 1000 °C/min

120
have been observed. A maximum temperature of 1700 °C, determined at the crucible bottom with an optical pyrometer, has

been measured. The furnace has great flexibility with regard

to controlled atmosphere and vacuum operation.

The author wishes to acknowledge Dr. J. L. Thompson for

contributing many of the basic concepts in the design of this

furnace. ( (D. K. Snediker)

3. Multiplex for Dual Spectra

a. Introduction. In order to improve the accuracy

of data taken with the NBS Drift-Free MSssbauer Spectrometer

[44], it is desirable to accumulate two spectra simultaneously

with the velocities provided by one electromechanical drive.

The data can be stored in the two memory halves of a multichannel analyzer. In this way, it is possible to take spectra

of a standard and a sample at the same time with both having

exactly the same velocity dependence. From the data taken

with the standard, a velocity calibration of the spectrometer

can be obtained, and this calibration can be used to express

the results with high accuracy.

b. Analyzer . The analyzer that is being used is an

RIDL 34-27*. The analyzer is operated in the time mode and

the analog voltage of its address scaler is used as the input

signal to the drive amplifier. A pulse is supplied to the

analyzer time base input in the time mode to initiate a memory

cycle and channel advance. This pulse begins the analyzer T s memory cycle program which is as follows:

(1) Add-1 (Time 1.5/^s) This part of the program adds

one count to the analyzer T s add-subtract scaler

if the temporary store bistable was set when the

analyzer was in the previous memory cycle.

For disclaimer of equipment and materials see last paragraph

of preface.

121
(2) Write (Time 2.5 /is) In this part of the program,

the data stored in the add- subtract scaler is

transferred into the proper channel location of

the magnetic memory.

(3) End of Program (Time 1.5 /is) This part of the

program acts as a delay in the time mode. At

the end of its delay it produces a channel advance

pulse (C.A.P.) which causes the address scaler

to advance one channel.

(4) Delay (Time 3 /is) Delays program cycle 3 /is while

address is advanced.

(5) Read (Time 2.5 /is) This is the last step in the

memory cycle and it transfers the data for the

new channel from the memory into the add-subtract

scaler.

c. Multiplex Logic . In order to lower the data accumulation time, the multiplex (figure 42) was designed so that the

memory of the analyzer would be used on a demand basis by the

two detector systems. This is done because the memory cycle

time of the analyzer is 12.5 /is. If the memory was not used

on a demand basis each pulse from either detector would require

a memory cycle and the dead time of the system would be increased.

In order to use the memory of the analyzer on a demand basis

the multiplex must specify when the analyzer is to change subgroups. When data is being accumulated in one subgroup (e.g.

for detector A) and a count comes in for the other subgroup

(detector B) the analyzer receives a pulse (Store Pulse) which

causes a memory cycle with a change of subgroup instead of a

channel advance. The store pulse is derived from the change of

state of bistable "A" which is triggered when a count which

should be stored in the other subgroup arrives from one of the

detector systems. The store pulse is introduced at the time

base input and the analyzer starts its program cycle.

122
To save the pulse that caused the memory cycle and store it

in the add-subtract scaler, it is necessary to delay the pulse

until the analyzer is in its memory cycle and then set the

temporary store bistable. When the analyzer goes through its

next memory cycle, the count will be added to the data for that

channel and stored in the memory.

DETECTOR

OUTPUT

§

INTER LOCK BISTABLE

B FIG. 44

INPUT DET

SYSTEM *l

ALL DIODES DR435

Figure 42

S

INPUT DET. SYSTEM *2

Multiplex

123
d. Logic to Interface Multiplex to Analyzer . In order

to operate the analyzer in the multiplex mode, it is necessary

to modify the program of the memory cycle slightly. There are

,

in fact, two program cycles necessary. When there is a pulse

from the time mode oscillator, the analyzer program cycle should

not be changed. When the analyzer receives a pulse from the

multiplex telling it to change subgroups (store pulse) , it must

initiate a memory cycle which does not have a channel advance

pulse after the End of Program. At this time the 200 bistable

in the address scaler should change its state to correspond to

the correct subgroup and the program should finish as in a normal cycle. The manner in which the second program is accomplished is to break the analyzer's memory cycle at the output

of the End of Program one-shot. This output is taken to the

interface and is tested by the C.A.P. gating circuit to see if

a time mode oscillator pulse had occurred before it. If a time

mode oscillator pulse had occurred, then the C.A.P. gate gives

an output and the channel is advanced. If a C.A.P. had not

occurred, the C.A.P. gate does not give an output, and the

program cycle is completed with a change of subgroup and without a channel advance.

e. C.A.P. Gating Circuit . The analyzer can be made

to go through a memory cycle by two events: (1) a store pulse,

and (2) a time mode oscillator pulse. Because the analyzer

could be in a memory cycle when the time mode oscillator pulse

arrives, it is necessary to insure that the analyzer will have

a channel advance. The channel advance pulse gating circuit

(figure 43) contains the necessary logic to accomplish this.

The time mode oscillator pulse triggers one-shots TT PTT and "Q TT and bistable TT C

TT . One-shot ,r P TT is set in order to inhibit the

output of gate "VTT which insures that bistable TT C" can be set

even in the presence of a C.A.P. If the analyzer is in a memory

cycle, tT C

t! can be set before or after the C.A.P. If C is set

before the C.A.P., then the analyzer will have a channel advance

and C will be reset. If TT C

n is set after the C.A.P., then the

124
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125
analyzer will continue to the end of its program cycle, and a

new cycle is initiated when one-shot "Q" returns to its stable

state. When the C.A.P. from this memory cycle arrives ,T C,T is

set. Therefore, the analyzer advances one channel and "C" is

reset. If the analyzer was not in a memory cycle when the time

mode oscillator pulse arrives then after a minimum of 8 jus delay

the memory cycle with a channel advance is initiated.

f

.

Interlock Circuit . The memory cycle program of the

analyzer would be disrupted if it received pulses on its time

base input while it was in a memory cycle. To insure that the

memory cycle is not disrupted, it is necessary to have an interlock circuit (figure 44) which inhibits all pulses to the time

base input while the analyzer is in a memory cycle. The circuit

works in the following manner. When there is a pulse at the

time base input of the analyzer, bistable B is set into the

state which inhibits and gate X until the end of time program

pulse which resets B.

Bistable "B" is also used to inhibit and gates Y and Z so

that the state of bistable A does not change during the analyzer

memory cycle. If TT Y,T and "Z" were not inhibited and if the

count rate on one side was much lower than on the other side,

the fast side would accumulate almost all of the time to the

complete exclusion of the slower side.

g. Conclusion . The Multiplex for Dual Beam Mossbauer

Spectroscopy was designed using Transistorized Building Blocks

for Data Instrumentation [46] with very few minor modifications.

The system when used with the NBS Mbssbauer spectrometer has

given good dual spectra. By the use of a sodium nitroprusside

standard absorber [41], the errors in the reproducibility of the

velocity have been reduced to 10" cm/s /month.

The author would like to acknowledge the assistance and

helpful discussions with R. W. Shideler and J. J. Spijkerman.

(F. C. Ruegg)

126
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TIME

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127

ii
4. Gas Flow Proportional Counter for Fe Mttssbauer

Spectroscopy

a. Introduction , The prerequisites for a detector for

Fe Mftssbauer spectroscopy are that the detector be able to resolve the 14*4 keV gamma ray and 6.3 keV x-ray, and be as insensitive as possible to the 122 keV and 136 keV gamma ray of the

nuclear energy spectrum of Co. Because of the low energy of

the 14.4 keV gamma ray of Mossbauer interest, a proportional

counter is an ideal detector to use.

b. Gas Flow Proportional Counter for Fe Mossbauer

Spectroscopy . At NBS, a Reuter- Stokes model RSG-30A*

proportional counter with a 90% xenon, 107o methane gas fill

was used in our MOssbauer experiments. After using this detector for about a year, it was decided to use a gas flow system

(figure 45) using 90% argon and 10% methane gas which has

several advantages over the sealed counter. The life of the

detector when >5 mCi sources are used is increased by many

orders of magnitude. The signal-to-noise ratio is improved

because the argon-methane gas is not as sensitive to the higher

energy radiations. The gas has a higher gain at 2000 volts.

c. The Proportional Gas Filling . The argon-me thane

proportional gas gives a much improved signal-to-noise ratio

for the 14.4 keV gamma ray because it is virtually insensitive

to the higher energy radiations. The signal-to-noise ratio for

the gas flow counter using the same geometry and detection system is approximately 3 times better than the signal-to-noise

ratio for the sealed Xe-CH, detector. The geometry is: (1) the

detector's Be window is covered by a 1/16-in lead backed with

1/6-in Al filter which has a .5-in diameter hole centered over

the Be window, (2) the Be window is 7 cm from a 5 mCi Co

source. Using this geometry, removal of the lead shield causes

the 14.4 keV gamma peak to be obliterated by the Compton scattering continuum in the case of the xenon-methane detector,

For disclaimer of equipment and materials see last paragraph

of preface.

128
while argon-methane flow detector continues to give a good

spectrum with a signal-to-noise ratio (figure 46) better than

the xenon-methane detector with lead shielding. The gas flow

counter when moved still closer to the source continues to give

a clean spectrum with a high signal-to-noise ratio.

d. Relative Efficiency of Two Gases . The relative

efficiency of the two counters is shown in figure 4 7 . The ' efficiency of the gas flow detector is 20% of the efficiency

of the Xe-Ch, counter at 14.4 keV. The poorer efficiency is

<e-£

h

DET.

f\

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P <?>

PRESSURE GAUGE

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REGULATOR

—£*3— NEEDLE VALVE

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Figure 45. Schematic of gas flow system

129
5 -

i—I—

r

WITH LEAD

SHIELD

NO LEAD

SHIELD

J L

t-i—i—i—i—i—i i r

SIGNAL

R = NOISE

OF 14.4 keV GAS FLOW DETECTOR

SIGNAL

NOISE

OF 14.4 keV OF SEALED DETECTOR

WITH SAME

GEOMETRY

4 cm FROM SOURCE

D NO LEAD SHIELD

ljU L III!

4.5

MILS Al FOIL

Figure 46. Plot of the signal-to-noise ratio of the gas

flow detector compared to the sealed detector

for the 14.4 MeV gamma ray

caused by the fact that argon is less dense than xenon and

hence it does not absorb as many 14.4 keV gamma rays. The

poorer efficiency can be compensated for by improving the

geometry of the argon-methane detector. Therefore it is possible with a 5 mCi Co source to handle more 14.4 keV gamma

rays with a higher signal-to-noise ratio with improved resolution using the argon-methane detector than using the xenonmethane detector.

e. Filter * Because of the large number of 6.3 keV

X-rays from the source, and because the two proportional gases

have a larger efficiency for the X-rays than for the gamma rays,

130
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131
it is advisable to use a filter like aluminum to decrease the

detector dead time resulting from the X rays. Figure 48 is a

graph of the relative intensities of the 14.4 keV gamma ray

and 6.3 keV X ray vs. the thickness of the aluminum filter.

f. The Gas Flow Detector . The gas flow detectors

that are being used are modified tubes which no longer worked

because the xenon-methane gas had been sufficiently degraded

by the high gamma flux. The modifications necessary to convert

them to flow counters are to drill two holes in the cylindrical

counter at each end diametrically opposed to the Be window,

and epoxy two bake lite inserts into the holes to provide an

input and vent for the argon-methane gas. It is also possible

to buy the flow detectors commercially.

g. The Detection System . The detection system is:

the proportional counter, model 31-24A RIDL preamplifier for

gas detector, model 30-23 RIDL double delay line amplifier

and a model 34-12 RIDL multichannel analyzer.* A picture of

a spectrum accumulated for .5 minutes of live time is shown

in figure 49.

(F. C. Ruegg)

E. Search for Sn Standard

The theoretical interpretation of the Mossbauer chemical

shift in tin has long been hindered by the lack of a standard

to which the chemical shift can be related. At present, aand 0-tin, Mg

2

Sn and SnO^ are all used as differential chemical

shift standards by various laboratories. Such a variety of

standards renders the task of comparing chemical shift data from

various laboratories virtually impossible. Furthermore, it is

at present impossible to calibrate a tin spectrum with respect

to velocity without changing the source to iron-57 and using

a Sodium Nitroprusside Standard Reference Crystal as the absorber. Such a procedure is not only inconvenient, but also

* For disclaimer of equipment and materials see last paragraph

of preface.

132
l Int

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Figure 48. Graph of relative intensity of the ratio

14.4 keV gamma ray to the 6.3 keV x-ray

versus thickness of the aluminum filter

133
bJ

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through 9 mil of Al foil. Source 1.5 cm from Be

window. Spectrum accumulated for .5 min live time

at 99% dead time.

resets the spectrometer unnecessarily. In addition, a tin

"standard" such as p-tin must be employed for differential

chemical shift, since sodium nitroprusside cannot be used for

this purpose in a tin system. It is desirable that a suitable

standard for differential chemical shift and velocity be developed for tin Mossbauer spectroscopy.

The MBssbauer spectrum of such a standard must have certain important characteristics:

1. The spectrum should be a doublet at all temperatures.

This characteristic is important because defining a

differential chemical shift relative to the midpoint

of the doublet gives an internally consistent point

of reference. Furthermore, the doublet provides a

means of velocity calibration. Since the tin lines

134
57

are wide, relative to the Fe lines, the splitting

of the doublet should be greater than the 1.6 cm/s

splitting of sodium nitroprusside by a factor of 2

to 2.5.

2. The standard should give a reasonably high percent

effect in order to expedite the standardization process.

In addition, the standard should have the following chemical characteristics:

1. Chemical stability with respect to air and moisture.

2. No long-term phase transitions, alterations in crystal

structure, or autocatalytic decomposition reactions

should take place.

3. Reasonably low toxicity.

4. Capable of a high degree of purification with respect

to tin-containing impurities.

The tin compounds for which spectra have been obtained by

the various laboratories engaged in tin-119 Mbssbauer spectroscopy have shown quadrupole splittings too low for use as

a standard (i.e., up to 1.6 mm/s). The quadrupole splitting

is related in part to the asymmetry of the ligands bonded to

the tin atom. Since tin does not form coordination compounds,

one is limited to inorganic salts , organo-tin compounds or

alloys and intermetallics . Compounds of the former types

possessing the necessary asymmetry are usually unstable and/or

liquid. Alloys and intermetallics present the difficulty of

phase effects , and to some extent difficulties in accurate

synthesis.

The development of this standard is being approached in

three ways. Tin compounds are being screened according to

chemical and physical characteristics. Spectra are being

obtained for all compounds meeting the previously discussed

criteria. The possibility of using admixtures of compounds

and/or alloys having singlet spectra with adequate splitting

135
is being investigated; and finally, the advice of persons

active in tin-119 Mossbauer spectroscopy is being solicited

with regard to suggested standards.

(D. K. Snediker)

F. Consultations

Dr. George Johns, Wright Field, Air Force Institute of

Technology

Dr. Edward Allard, ERDL, Fort Belvoir

Dr. Serge Vinogradov, Yale University Medical School

Mr. Alfred Jakniunas , Biomedical Electronics Consultants,

Inc.

Mr. Alan Michels, Radiation Instrument Development

Laboratories

Dr. Rolf Herber, Rutgers University

Dr. Hobson, University of Richmond, Virginia Institute of

Scientific Research

Mr. William Grote, Frazier Institute

Prof. P. C. Lall, Howard University

Mr. Robert Weiss, Nuclear Science and Engineering Corp.

136
G. Publications

1. DeVoe, J. R. , and Spijkerman, J. J., "MBssbauer Spectrometry," Anal. Chem. 38, 382R-393R (1966).

A review of the applications of MBssbauer spectrometry

to chemical analysis, and a bibliography of publications on these applications in 1965 are presented. The

principle of the spectrometer as well as a discussion

of errors associated with its use are described. Current theoretical interpretations of some aspects of

the MBssbauer spectrum are discussed. Chemical structure analysis is the most prevalent application to date,

and other applications, such' as metallurgy and quantitative analysis, appear to be promising.

2. DeVoe, J. R. , and Spijkerman, J. J., "MBssbauer

ADDlications in Aerospace," Proceedings of Symposium

on Radioisotope Applications in Aerospace, Dayton? Ohio, February 1966, to be published.

The principle of the MBssbauer effect will be discussed.

A few possible applications of the technique with

respect to physics and engineering in aerospace will

be outlined. Of greater interest are the possible

applications of the technique for determining chemical

structure and solid state properties of materials.

Solid phase transitions of materials subjected to severe

conditions similar to that existing in space can be

measured by MBssbauer effect.

The National Bureau of Standards' MBssbauer spectrometer

will be discussed and some data taken on a number of

materials (such as tecktites, steels, glasses, and

metal alloys) will be presented.

3. Ruegg, F. C. , Spijkerman, J. J., and DeVoe, J. R.

,

"A MBssbauer Spectrometer for the Structural Analysis

of Materials," Proceedings of the International Atomic

Energy Agency Symposium on Radioisotopic Instruments

in Industry and Geophysics, Warsaw, Poland, Oct. 1965,

to be published.

A MBssbauer Spectrometer has been designed to provide

high precision MBssbauer spectra. The instrument uses

two electromechanical transducers, one driver and one

sensor, in a feedback loop which incorporates an

operational amplifier and a power amplifier. The

transducer system is coupled to the scaler input of a

multichannel analyzer. A high degree of synchronization between the channel number (which represents units

of velocity) and the actual velocity produced by the

137
transducer is obtained by using the analogue voltage

of the channel number as the input to the electro-;

mechanical system. By advancing sequentially the

channel number as a linear function of time, a motion

of constant acceleration is produced. Gamma rays from

the radiation detector proportional counter of Nal(Tl)

are then energy selected by a single channel pulse

height analyzer and these pulses are presented to the

multiscaler input. The spectrometer can be used to

accept high counting rates by using a units scaler

with a ten megahertz response.

The spectrometer can be used with a variety of auxiliary

equipment such as to measure spectra at low temperature

or high pressure.

4. Snediker, D. K. , "The Mbssbauer Effect of Sn119 in

Palladium-Rich Palladium-Tin Solid Solutions,"

Mossbauer Effect Methodology, Vol. 2_, Plenum Press,

New York, in press.

A study of the palladium-rich end of the palladium-tin

alloy system has been conducted using the Mossbauer

effect of Snll9m. Alloy absorbers of composition from

1 to 16 atom 7 tin and the intermetallic Pd~Sn were

studied.

The Mossbauer parameters, e. g. fractional effect,

half-width and chemical shifty are reported for the

various compositions. The Mossbauer spectrum of the

alloy absorber has been determined to be a doublet

consisting of spectra with chemical shifts corresponding to PdoSn and the Sn-Pd solid solution.

new source with a composition corresponding to Pd~Sn

is synthesized. Using this source with a J3-tin

A

was

absorber a spectrum was obtained with a half-width of

0.08 cm/s and an effect of 24%.

5. Spijkerman, J. J., Landgrebe, A. R. , and Ruegg, F. C.

,

"Mbssbauer Effect in Ethylenediaminetetraacetatoiron

III Compound," Presented at American Chem. Soc. Meeting

September 1965.

The Mbssbauer effect was used to investigate ethylene^

diaminetetraacetato complexes of iron (III). The EDTA

complex of iron, M(FeEDTA) , was investigated for compounds where M was H, Li, Na, NH, , K, and Cs. The

spectra of the powered compounds were obtained at 21

and -130 °C. Two distinct chemical shifts were obtained indicating the iron complexes are in two chemical environments. The chemical shifts were positive

138
with respect to the NBS MSssbauer standard reference,

sodium nitroprusside. The iron is definitely in the

plus III valance state. Tentatively, we believe the

iron to be in the octahedral configuration in the

solid acid while the anion of the acid is in the pentagonal bipyramidal structure.

6. Spijkerman, J. J., Landgrebe, A. R. , Ruegg, F. C.

,

DeVoe, J. R. , "The Use of Mdssbauer Effect to Study

the Adsorption of Iron on Cationic Ion Exchange Resins,"

Presented at Am. Chem. Soc. Meeting, September 1965. ' The purpose of this study is to describe a capability

of MBssbauer Spectroscopy to provide significant information regarding the structure of a wide variety of

chemical systems. The chemical process and bonding

of iron to cationic ion exchangers was investigated.

The ion exchange resins investigated were : Duolite

C-10, Dowex 50, CG-50, and Bio-rex 63. Spectra were

taken at 25 and -130 °C. The isomer shift in all

cases was shown to be characteristic of iron (III) ion.

Spectra were obtained for Dowex 50 of various cross

linkage and moisture content. The spectrum for the

iron in Dowex 50 at room temperature , shows two

closely-spaced peaks which indicate a small quadrupole

interaction. Comparison of the Dowex 50 spectrum at

the two temperatures with other data suggests that the

iron is present as

\n9 0). Fe^H >e (H9 0)

X

Other corroborating evidence for the above structure

is the absence of magnetic interaction to -130 °C.

7. Spijkerman, J. J., Ruegg, F. C. , DeVoe , J. R. , "Standardization of the Differential Chemical Shift for

Fe57

}

Tf MBssbauer Effect Methodology, Plenum Press

(1965) pp 115-120.

To provide MBssbauer data for Fe on a uniform basis,

to eliminate recalculation of data from various laboratories, and to provide tables of M5ssbauer spectra, the

National Bureau of Standards has included disodium

pentacyanonitrosylferrate dihydrate, Na2[Fe(CN)5NO]»2H

2 in the Standard Reference Materials Program. Single

crystals of sodium nitroprusside will be available by

April 5, 1965, for this standardization. The crystals

are supplied by a commercial manufacturer, and calibrated by NBS on a MSssbauer spectrometer, using an

optical fringe counting technique.

139
The Mossbauer spectrum of a single crystal absorber,

cut along the be plane, is a well resolved, symmetric

doublet. The center of this doublet is defined as

zero reference point for the differential chemical

shift, with the containing absorber at 25.0 °C. The

absorber crystals supplied will be 1 cm x 1 cm with

25.0 mg/cm2 of natural iron.

8. Spijkerman, J. J., Ruegg, F. C, May, L. , "The Use of

Mossbauer Spectroscopy in Iron Coordination Chemistry,"

Mossbauer Effect Methodology, Vol. 2^, Plenum Press,

New York, in press.

The application of Mossbauer spectroscopy to the study

of iron coordination chemistry is discussed. The

chemical shifts of iron compounds are adjusted to the

new standard, sodium nitroprusside, and this differential chemical shift is correlated with the 4s electron

contribution to the bonding in the compounds. A new

interpretation of the chemical shift - 4s electron

contribution diagram is proposed including the latest

results of Molecular Orbital calculations. The quadrupole splitting is related to the total spin and

structure of the compound. The asymmetry of the

doublet intensities can be used to obtain additional

information about the structure of the compound and

the spin-spin relaxation time. The relationships

between the Mbssbauer parameters and the data from

other spectroscopic measurements are discussed.

140
5. RADIOISOTOPE TECHNIQUES

A. Facilities

New laboratories have been recently equipped by the radioisotope techniques group at Gaithersburg. The new facilities

consist of a nuclear instrumentation room, a darkroom, and two

radiochemical laboratories. The present laboratories used for

this work will be replaced in the future with laboratories

designed to handle higher levels of radioactivity.

The nuclear instrumentation room contains automatic proportional, gamma and liquid scintillation counting systems and a

radiochromatographic scanner for counting thin layer and paper

chromatograms (see figure 50). This room constitutes a pool

of radiation counting equipment of which the liquid scintillation counter belongs to the Organic Chemistry Section.

Figure 51 shows half of a double radiochemical laboratory

module with an apparatus used for controlled potential coulometric analysis. Against the back wall is a glove box which

contains the cells in a nitrogen atmosphere. Figure 52 shows

the other half of this laboratory which is suitable for work

on substoichiometric radioisotopic dilution analysis.

A standard double module which has been modified for the

application of radiometric and chromatographic procedures is

shown in figures 53 and 54. A hood which is suitable for

radiochromatographic separations, an area for large developing

tanks, and thin layer chromatographic tanks can be seen in

figure 53. A paper chromatographic developing system mounted

on an aluminum flexaframe, a polyethylene hood used for spraying chemical reagents, and a hood where the radiometric precipitation can be performed are shown in figure 54.

(A. R. Landgrebe)

141
Figure 50. Nuclear instrumentation room containing

automatic proportional and gamma counting

systems

142
Figure 51. Radiochemical laboratory module for

subs toichiome trie radioisotopic

dilution (SRDA)

B. The Application of Radioactive Isotopes to the Quantitative

Analysis of Trace Amounts of Inorganic Substances on Paper

and Thin Layer Chromatograms

1* Introduction

The basic techniques involve the following steps: (1) Evaporate a solution of the unknown mixture on a sheet of filter

paper or a thin layer plate forming a spot near one end. The

sample size may vary from 0.001 milliliter up to several milliliters. (2) Allow a suitable solvent to pass lengthwise

through the paper starting near the spot. If the solvent is

chosen correctly, the various components will be moved at different rates by the solvent. Ideally, each component will form

143
fet

Figure 52. Other half of SRDA laboratory

144
a spot at a different place on the chromatogram. (3) After

the solvent has moved to the other end of the sheet it is

allowed to evaporate. (4) After separation of the ions, qualitative detection can be accomplished through the use of chemical

reagents or radioisotopes. The chemical method of detection is

based on the substance reacting to give colored or fluorescent

spots. Some of the methods of detection using radioisotopes

are autoradiography, automatic scanners with a proportional)

detector for beta emitters and Nal (Tl) well counters for gamma

emitters. After having established the R

f factors, the last

step (5) in the analysis is the quantitative determination of

Figure 53. Radiometric laboratory

145
Figure 54. Radiometric laboratory

the elements of interest on the chromatograms. Analysis by

means of radioisotopes can be performed by activation analysis,

isotopic dilution analysis, radiometric precipitation (R.P.)

or exchange of a radioactive reagent with a substance of interest. Examples of the quantitative determination of trace constituents by radiometric precipitation (R.P.) or exchange of a

radioactive reagent will be treated in this paper. The latter

will be called radiometric exchange analysis (R.E.)

The literature on inorganic separations on paper and thin

layer chromatography is quite extensive but the studies are

incomplete with a few notable exceptions [47,48]. In this study

146
we wished to separate the elements completely in order to test

the radiometric precipitation methods which were developed;

therefore, the separations which were developed are rather

selective.

Van Erkelens [49] mentions the possibility of performing

quantitative analysis of traces of metals separated by paper

chromatography. He precipitated the elements in the chromatograph with radioactive hydrogen sulfide, but gave no data whereby the sensitivity or precision of the method could be estimated.

In another paper [50], Van Erkelens described an analysis for

32 lead, using phosphate labeled with ' P, after separation from a

number of interfering elements. This method was extended by

Welford [51] and showed high sensitivity, but again no data were

presented on the precision of the methods. The analysis of

iron, copper and manganese has been accomplished by precipita32 tion with P labeled phosphate in our laboratory.

Radiometric precipitation can be described by the equation:

A + X* = A X*

s The procedure is very similar to other types of precipitation.

The radioactive precipitating agent (X*) is added to A, the

cation, to be determined. Then the precipitate AX* is separated

from excess X*. In principle, either the excess of X* or AX*

s should be counted, but in practice it is found that AX* should

be counted. It is to be noted that no measurement of mass in

the actual radiometric procedure is required. The sensitivity

of this method depends on the K , the concentration and specific activity of X*, the precipitating agents.

A method of analysis has been developed, on the basis of the

59 exchange of Fe with insoluble ferrocyanides , for example:

3M2[Fe(CN)

6

] + 4 Fe*+3 = Fe* [Fe(CN)

6

] 3

+ 61^

There are a great many elements that form insoluble ferrocyanides. The theoretical limit of detection of the following

insoluble ferrocyanides is 1.9 jig for manganese, 0.009 jig for

147
cobalt, 0.008 fig for nickel, 0.003 fig for copper, 0.005 fig for

zinc, 0.001 jag for gallium, 0.04 fig for silver (Ag

3 [Fe(CN)

6

])

,

0.025 jig for cadmium, 0.000004 fig for indium, 0.04 fig for lead

and 0.028 fig for the uranyl ion. The figures obtained for the

limit of detection are based on solubility product considerations for the conditions used in this report.

The radiometric exchange analysis (R.E.) can be generalized

by the following equation:

AX, n + B* = B* X, ^ + A

The signs are omitted for simplicity. The procedure involved

the addition of the radioactive cation to the precipitate and

required the isolation of B*X, v from excess B*. If the amount

of activity isolated is proportional to the amount of AX, \

then a method of analysis is available. This procedure also

requires no measurement of mass in the radiometric method and

the activity measured could be B* at equilibrium or B*X, s

.

The sensitivity depends on the K , of AX, n and B*X, s. The

sensitivity is also dependent on the specific activity of the

reagent B* and upon its concentration.

The usefulness of the radiometric method of analysis for

iron, cobalt, copper and manganese will be demonstrated in this

work by its application to NBS Standard Reference Material

No. 671, nickel oxide, which contained traces of these metals.

2. Experimental

a. Reagents and Purification. Purification of Paper : The chromatographic paper,

Whatman No. 1, was purified by washing with 3N hydrochloric

acid. The acid was allowed to migrate down the paper. The

paper was washed downflow with water (3 times) and air dried.

Solvent Preparation : 1. Methyl ethyl ketone - HC1: 8 parts concentrated hydrochloric acid was added to 92 parts

methyl ethyl ketone.

2. n-Butanol - HC1 - ethyl acetate: 25 parts

148
hydrochloric acid was added to 30 parts nButanol and 45 parts ethyl acetate* Prior to

use, the solvent was thoroughly mixed.

3. n-Butanol - HBr: 50 ml of concentrated hydrobromic was mixed with 50 ml of n-Butanol.

4. NH^OH-NH^Cl: pH = 10. 142 ml of concentrated

ammonia solution was added to 250 ml of water

containing 17.5 g of ammonium chloride.

5. Carbon tetrachloride - benzene: 50 parts of

carbon tetrachloride was added to 50 parts of

benzene

•

6. Sym-collidine - 0.4 M HN0

3 (100 ml) of 2, 4, 6

trimethylpyridine is shaken with 0.4 N -nitric

acid (100 ml); the heat generated by the mixing

causes the temperature to rise. When the mixture cools to 25 °C the layers are separated.

The organic layer is saved for use and the

aqueous layer discarded.

Spray Reagents

1. Diphenylcarbazide - a 1% solution of diphenylcarbazide in 95% ethanol was prepared.

2. Dithizone - CC1, - a 0.05% solution of dithizone

4

in carbon tetrachloride was prepared.

3. Quinalizarin - a 0.005% solution of quinalizarin

in 95% ethanol was prepared.

4. Sodium hydroxide - a IN solution of sodium

hydroxide was prepared.

5. Ammonia - a glass chromatographic tank was

saturated with ammonia vapor by placing four 100-

ml beakers containing concentrated ammonia in

the bottom of the tank.

6. Dithizone - (CH

3

) 2

C0 - a 0.05% of dithizone in

acetone was prepared.

7. Alizarin - a 0.05% solution of alizarin in 95%

ethanol was prepared.

149
8. Dimethylglyoxime - a 5%. solution of dimethylglyoxime in 95% ethanol was prepared.

9. Tetrahydroxyquinone - a 5% solution of the

disodium salt of tetrahydroxyquinone in 95%

ethanol was prepared.

10. Morin (3, 5, 7, 2', 4

T pentahydroxyflavone)

- a 0.01% solution of morin in 95%, ethanol

was prepared.

Radioisotopes

*2 —

1. P - labeled phosphates. A solution of radioactive trisodium phosphate was prepared so that

the phosphate concentration was 0.12M and con5 32 tained 10 cpm of P per ml.

2. Co obtained from ORNL with a specific activity

of 5.4 x 104 mCi/g was used. 106

cpm of 60Co

per ml was used in all experiments.

59

3. Fe obtained from Nuclear Science and Engineering Corporation with a specific activity of

3

59

x lCf* mCi/g was used. 10 6

- 105 mCi cpm of

Fe per ml was used in all experiments.

Metal Test Solution : The stock solutions had a concentration of 10 mg per ml and were diluted to

the desired concentration for qualitative and

quantitative analysis.

NiO Standard Reference Materials : 10.000 g of

nickel oxide was dissolved in 9M hydrochloric

acid. The final concentration of nickel oxide

was 0.1000 g per ml.

12 h Steel Sample : 5.000 g of 12 h steel was dissolved in 6M hydrochloric acid containing a

few ml of nitric acid. The final concentration

of the steel sample was 0.0500 g/ml.

Cu-Be Alloy : The Cu-Be alloy was dissolved in 6M

nitric acid. The final concentration was 0.1000

g per ml.

150
Potassium Ferrocyanlde Solution ; The potassium

ferrocyanide was dissolved in 100 ml of distilled water and after stirring for a few hours

the excess salt was filtered.

NaOH-HpOo Solution : 90 ml of 0.1N sodium hydroxide

was added to 10 ml of 30%, hydrogen peroxide.

Metal Dithizonates : A 0.1% solution of Co, Ni, Cu,

Zn, and Fe were extracted with an equal volume

of 0.1% dithizone. The separated chloroform

was washed with 0.02N nitric acid to remove the

excess of dithizone.

b. Separation Procedures . Methods of separation were

developed using synthetic solutions of the ions of interest as

well as solutions of the samples. The procedure used to separate the ions in the nickel oxide, Cu-Be alloy, 12 h steel and

metal dithizonates consisted of spotting several 0.01 ml aliquots of the original samples on the Whatman No. 1 chromatographic paper or on the thin layer plates. With the papers,

descending chromatography was used and with the thin layer

plates, ascending chromatography was used. The papers or TLC

plates were removed from the chromatographic tanks, air dried,

and placed in a tank saturated with ammonia vapor in order to

neutralize the acid used in the separation. The papers were

removed from the tank and air dried again.

The separation of the steel was performed by two-dimensional

chromatographic methods. The initial separation was accomplished with methyl ethyl ketone -HC1 and then the molybdenum

plus iron, located at the solvent front, was separated with

ethanol-HCl solvent in a second dimension. The paper was cut

below the solvent front prior to the second separation. Using

sym-collidine and 0.4 HN0~ as a solvent an improved separation

of the chromium and nickel could be obtained in the steel samples. The separation with the 12 h steel was accomplished by

first separating the samples with methyl ethyl ketone-HCl,

neutralizing the hydrochloric acid with ammonia vapor, air

151
drying, and separating down flow with the sym-collidine solvent

in the same direction as the original solvent,

c. Qualitative Detection , The procedures for the use

of spray reagents can be found in text books on paper or TLC

chromatography [52,53 ]. The ions were detected with the

appropriate spray reagents listed in table 17

The Rf factors of gamma emitters have been determined using

the Nal (Tl) well counter. An automatic scanner with a 2ir

proportional detecting system for beta emitters on thin layer

plates or kir proportional detecting system for beta emitters

on paper chromatograms has been used. When quantitative determination of the radioactivity present in a chromatogram is

desired, an automatic sample changer with a well type Nal (Tl)

scintillator (gamma emitters) or proportional counter (beta

emitters) was used for counting segments of the paper or thin

layer which provide sufficient resolution of the chromatographic

peaks.

d. Quantitative Analysis . The following procedures are

32 used for the radiometric precipitation with P labeled phosphate: The phosphates of iron, copper, and manganese were precipitated with radioactive trisodium phosphate in 50 ml beakers.

The papers were removed, washed with water and air dried. The

labeled precipitates were assayed with low background proportional beta counting systems.

The following procedure was used for the radioactivity

exchange method of analysis for manganese: The manganous ion

was oxidized with alkaline hydrogen peroxide, washed with water,

and air dried. The papers containing the manganese dioxide were

equilibrated with a solution containing a Co in an ammonium

hydroxide -ammonium chloride buffer, pH 10.00. Standards were

60 prepared in the same way. The Co was assayed using a scintillation Nal (Tl) well counter. As the amount of manganese

dioxide on the paper is increased, more of the Co is removed

from solution.

152
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153
The following procedure was used for the radioactivity

exchange method of analysis of nickel, copper, cobalt , manganese, cadmium, zinc, and mercury. The ions were precipitated

by reacting them with a saturated solution of potassium ferrocyanide. The papers were then washed with water, 0.1 N hydrochloric acid and water again. The papers were equilibrated

59 with Fe solution, washed with water, dried and counted using

a scintillation Nal (Tl) well counter.

In all cases, the method of washing was standardized to

give the lowest possible blank. Three to five milliliters are

placed in the beakers along with the papers containing the

ferrocyanide precipitant. After swirling for one minute the

water was decanted and this procedure was repeated two more times.

The quantitative analysis of the nickel oxide sample was

accomplished by the following procedure. After having established the R

f factors and, therefore, the relative position of

the separated elements on three of the chromatograms , the corresponding areas on additional chromatograms were cut out and

analyzed quantitatively. Iron, copper and manganese were

determined by radiometric precipitation with labeled phosphate.

The manganese was also determined by the radioactivity exchange

method of analysis described above. Cobalt was determined by

the radiometric exchange method with the ferrocyanide procedure*

3. Calculations

Blanks were subtracted from all data for each element and

« standard curves were prepared by plotting cpm isolated on the

paper versus fig added. The experimental points were fitted to

a straight line by least squares analysis.

4. Results and Discussions

Separations were developed for trace constituents in Cu-Be

alloys containing Sn, Fe, Cu, Zn, Co, Ag, V, Be, Al, and Pb;

for the metal dithizonates of Fe, Zn, Ni, Cu, Co; traces of Cu,

Mo, V, Ni, Cr and Mn in Standard Reference Material 12 h steel

and for nickel oxide containing traces of Fe, Cu, Co, Mn, Ti,

154
Cr, Al, and Mg. The R

f factors are listed in figure 55.

The separation of the Cu-Be alloy with n-Butanol-HBr required

fifteen hours and with the methyl ethyl ketone-HCl four hours.

The separation of the nickel oxide sample with methyl ethyl

ketone-HCl required three hours. The separation of the metal

dithizonates with chloroform-benzene solvent system requires

less than an hour. Due to their color, no qualitative detection is necessary with the dithizonates. The 12 h steel sample

was separated on paper and TLC plates. The time required for

paper chromatographic separation is eight hours and for the

thin layer chromatographic separations, five hours. With the

nickel oxide sample a separation of Mh, Co, Cu and Fe was

obtained and all the trace constituents in the 12 h steel have

been isolated using the three solvent systems as already explained. Only a partial separation was obtained with the CuBe alloy and the metal dithizonates.

From the limited amount of systematic work which has been

done, few definite conclusions can be drawn. It seems best to

have the matrix at the origin if possible, since the separations

are sharper and the blank in the subsequent analysis is lower.

The lack of a thorough understanding of the processes involved in the separation of ions on paper or thin layer plates

has led to an empirical approach to the choice of suitable solvent mixtures. The complexity of the processes involved in

paper and thin layer separation can be seen in the variables

concerned, all of which are interrelated. The main factors

concerned in the separation of cations are as follows: the

nature of the inorganic compound functioning in the process,

the type of solvent, the water content of the solvent and

humidity of the surrounding space, the acidity of the mobile

phase and of the original solution of the salt, the interference

of one cation with the movement of the other, the presence of

certain anions, the time of running of the chromatogram, the

temperature, and the condition and properties of the cellulose

or silica gel support.

155
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156
In table 17 are listed a number of colorometric spray reagents and the color of the ion detected. The dash indicates

no detection when the amount present was 1 fig. The tetrahydroxyquinone reagent is recommended for the detection of Cu

and Fe, ammonium sulfide reagent for Ag and Co, the diphenylcarbazide for Sn, dithizone for Zn and Pb, and alizarin for the

detection of Be and Al. The use of these chemical methods for

qualitative detection is rapid and allows one to screen metnods

of separation but they are not very selective or highly sensitive with the exception of some fluorescent methods.

The use of radioisotopes has several advantages over the

chemical methods of detection, such as the higher specificity

and sensitivity of radioisotopes. These advantages are sometimes offset by difficulties in detection of the radioactive

substance. Some of the difficulties are the blank problem and

and the ability to distinguish between two radionuclides which

were only partially separated. The use of the radioisotopes

for qualitative detection has the added advantage of making

quantitative yield corrections possible. The yield correction

is important when the ions of interest are entrapped in the

matrix and only part of the substance is recovered.

The radiometric phosphate procedure has been used to analyze

iron, copper and manganese, the sensitivity of the method being

0.1 fig for iron and copper. The procedure is not recommended

for manganese due to the poor precision obtained. The limit of

detection seems to be limited by the blank. This procedure

should be very sensitive for Th and U09« 59 The exchange reaction of Fe with insoluble ferrocyanides

has been used to determine Ni and Cu with a sensitivity of 0,1 fig,

Co with a sensitivity of 0.01 fig, Mn to 1.0 fig, Cd to 0.04 fig.

Preliminary data indicate that Zn, Pb, Ga, In and uranyl ions

can also be determined by this method.

Titanium, zirconium, hafnium, bismuth and thorium form insoluble ferrocyanides, but not enough information is available

157
to make a prediction as to the limit of detection. The alkaline

earths (except beryllium) , yttrium, lanthanum, actinium, and

the cerium earths can be precipitated from aqueous solutions to

which ethanol has been added. It may be possible to analyze for

these elements using a mixed solvent system. Almost all the

metal ferrocyanides are insoluble in the higher alcohols with

the exception of the hydroferrocyanic acid. Niobium, tantalum,

chromium, molybdenum and tungsten form insoluble ferrocyanides

,

but the rate of formation is slow, and complex anionic species

of these ions which are likely to be present make the use of

the radioactivity exchange analysis method rather difficult.

The stoichiometry is not known for many of the insoluble

ferrocyanides. The stoichiometry may vary with pH and other

conditions, for example the following cobalt species have been

isolated with ferrocyanide [Co(NH

3

) 6] +3

, [CoCNHj^O]*3

, [Co(NH

3

) 5 C1] +2

, [Co(NH

3

) 5

N0

2

]

+2

, [Co(NH

3

) 5

N0

3

]

+*.

A number of the elements form double salts, for example:

5[U0

2

] 2 [Fe(CN)

6

]

* 3 K

4 Fe(CN)

6

. Table 18 lists the results obtained for the analysis of the

nickel oxide sample. The amounts analyzed were 3.9 fig of iron,

2.0 fig of copper, 3.1 fig of cobalt, and 1.3 fig of manganese.

The data show quite satisfactory precision and accuracy for all

except the labeled manganese phosphate precipitate.

The precision of the analysis using radioactive tracers can

be affected by a number of factors, some of which are: (1) the

type of support media used and the impurities in this support,

(2) the interaction of the cellulose or silica with the separated ions or the precipitating agent, (3) the solvent system

used in the separation. The separation must be complete because

in most cases the selectivity of the method is based on complete

separation. The amount of material taken may also affect the

precision. If interferences exist or the elements are not recovered completely, yield corrections and a method of standard

addition must be applied along with the blank corrections.

158
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159
The precision of the radiometric method compares favorably

to most methods applied to paper or thin layer chromatography.

The precision does not compare as favorably to other methods

in general at the fig level but it must be remembered that this

is a micro as well as a trace method.

The accuracy can be affected by the following factors

incomplete separation, entrapment of the element to be analyzed

in the matrix, impurities in the paper, solvent, or from the

environment. The experimental procedures used in preparation

of the calibration curve and of the sample must be the same.

The accuracy can be improved by using the proper correction

factors when needed, such as yield and blank corrections. The

accuracy does compare favorably to that of other methods.

The sensitivity of these radiometric methods is high. The

sensitivity is limited by impurities in the system and from the

environment* The blank is larger when the major matrix component is moved to the solvent front. The sensitivity is limited

by the solubility product constant and/ or the equilibrium

constant of the exchange reaction. The specific activity and

concentration of the radiometric reagent will also affect the

sensitivity. Since these methods were developed for the determination of the separated components on a chromatogram, the

sensitivity is limited by the amount of material taken for

analysis, i.e., micro amounts. Other methods of separation

which use larger amounts of sample could be used as well as

preconcentration prior to chromatographic separation, thereby

increasing the sensitivity of the method.

The main advantage of the paper chromatographic method is

that it permits the analysis of a large number of elements in

the same sample. The radiometric methods which are used to

determine the separated elements have a greater sensitivity than

most other methods of quantitative analysis which are applied

to chromatographic separation on paper or thin layer plates.

(A. R. Landgrebe and T. E. Gills)

160
C. Differential Controlled-Potential Coulometry Utilizing

Radioisotopic Tracers

1. Introduction

During the past year a differential method of analysis was

developed. It consists of a controlled-potential coulometric

procedure in which two identical electrolytic cells are connected in series. Under prescribed conditions the same amount

of the element of interest is deposited in each cell. This'

permits the application of a technique called substoichiometric

radioisotope dilution.

The procedure involves the addition of a known amount of the

element to be analyzed to the control cell which is held at a

constant-potential and an unknown amount to the sample cell.

The addition of an equal, known amount of a radioisotope of that

element to each cell then follows. Since the same amount of

element is deposited in each cell, the difference in the amount

(differential) may be determined by measuring the radioactivity

left in each of the cells after a finite electrolysis time. The

relationship derived from the radioisotopic dilution principle

of radioactivity balance can be written in the form

aM = M — — (1)

a

t - a

2

where aM is the differential, M is the known amount added to the

control cell, a, and a2 refer to counts per minute of a radioisotope of element M left in the control and sample cells, respectively, and at is an equal amount of radioactivity in counts

per minute added initially to each cell. In order to obtain

independent verification of the series controlled-potential

method and to establish a means of comparison to the radioisotope technique, another approach was devised which consists

of a current integration procedure.

For the current integration procedure to be applied each

cell must contain identical reference electrodes. This is also

desired in that preelectrolysis of the supporting electrolyte

and sample solutions can be accomplished in each cell prior to

161
the start of the actual experiment. Since mercury was the

cathode used in this study, preelectrolysis is necessary in

order to remove traces of atmospheric oxygen which is reduced

at the mercury electrode in two steps:

1. 2H+

+

2

+ 2e~ = H

2 2

E = -.1 volt versus the Saturated Calomel Electrode (S.C.E.)

2. 2H+

+ H

2 2

+ 2e~ = 2 H

2

E = -.9 volt vs S.C.E.

After the removal of oxygen, potential control is transferred to the control cell and maintained at a value where the

only reaction that occurs at the mercury electrode is M

n

+ ne~

+n = M (Hg) . The current arising from the reduction of M will

-kt follow the equation i. = i e where i is the current just

prior to the start of the electrolysis, i. is the current at

any time, and k is the cell constant. The cell constant, k,

is unique for each particular cell geometry and is a function

of the electrode area, volume of solution, rate of stirring,

and the temperature. The current at any time is related to the

concentration of metal ion in the bulk of the solution. Integration of this current-time data yields coulombs which are

related through Faraday T s law to the amount of metal ion electrolyzed. Precise and accurate integration of this electrolysis

current is accomplished by developing a voltage across a stanr

dard resistor (see figure 56). This voltage is converted to

a frequency by means of a voltage-to-frequency converter. The

converter produces output pulses at a rate precisely proportional to the input voltage. These pulses are recorded on a

scaler. The data thus obtained consists of the integral of

the current -time curve.

Since the potential of the cathode of the control cell is

maintained at a value such that only the desired electrochemical

reaction occurs, attention may now be drawn to the sample cell

cathode potential. Here it is also important to maintain the

desired electrode reaction with the exclusion of all others.

The potential of the cathode in the sample cell will determine

162
CONTROL CELL

o

STANDARD

RESISTOR

AMMETER

VOLTAGE TO

FREQUENCY

CONVERTER f

SCALER TIMER &

CIRCUIT IN SERIES

Figure 56. Schematic diagram for differential

controlled-potential coulometry

the specificity of the electrode reactions. This potential

is governed primarily by (1) the current density in the sample

cell and is dependent on the control cell concentration,

(2) the concentration present in the sample cell, and (3) the

cell constant, k. To exclude undesired electrode reactions,

the sample cell cathode potential must be equal to or more

anodic than the control cell cathode potential. This can be

accomplished by providing a concentration in the sample cell

which is equal to or greater than that in the control cell.

An actual study of the potential of the sample cell cathode

was made and appears in the results section of this report.

2. Experimental

a. Apparatus . A diagram of the electrolysis cells

employed is shown in figure 57. Both the control and sample

cells are identical.

The anode consisted of a platinum wire bent in the shape

of a helix and isolated from the solution by a "Thirsty"* vycor

* Corning Glass Co. For disclaimer of equipment and materials

see last paragraph of preface.

163
glass tube abaut 9 mm x 5 1/2 in. The glass tube was of low

electrical resistance. The reference electrodes used were

identical saturated calomel electrodes of the commercial type

with a porous pin liquid junction. The cathodes were mercury

pools about 7 cm in area* Stirring of the solution and pools

was accomplished by means of a glass stirring rod fitted to a

synchronous motor assembly and rotated at 1800 r/min. The cell

cap was fabricated from lucite of one inch thickness. In addition to the holes drilled for the anode, reference electrode,

stirrer, and nitrogen inlets, a hole drilled diagonally permitted the introduction of sample solutions into the cell without removal of the cap. This provision was convenient In that

a positive nitrogen pressure could be maintained inside the

cell while solutions were being Introduced.

POTENTIOSTAT

CONTROL CELL SAMPLE CELL

Figure 57. Diagram of apparatus

164
For studies at the microgram level, the entire cell assembly was enclosed in a dry box made of durable plastic and was

filled with nitrogen prior to the start of the experiment.

Withdrawal of the solutions from the cells was accomplished by

inlets in each cell which were attached to a common vacuum pump.

b. Instrumentation. The potentiostat used in these

experiments was built according to the design of Connally and

Scott as described in their report [54]. The current integration equipment consisted of a voltage-to-frequency converter,

scaler, timer, and constant -current calibration source. Counting equipment consisted of an automatic sample changer and

scintillation counter with a well-type Nal (Tl) crystal. Potentials were measured with a millivolt potentiometer.

c. Reagent

s

. Stock solutions of cadmium were prepared

by dissolving high purity cadmium metal (99.997o) in a minimum

amount of concentrated HC1 and filled to volume with distilled

water in volumetric flasks. The distilled water was purified

by passing it through a mixed bed ion exchanger. The supporting

electrolyte was prepared by dissolving analytical reagent grade

potassium nitrate in distilled water. Further purification of

this solution when required was accomplished by electrolysis at

controlled-potential at -1.0 volt vs. S.C.E. A cadmium-109

stock solution was prepared by dilution of a 5 mCi cadmium-109

solution of high specific activity. Working solutions were

prepared by dilution of the appropriate volumes of the cadmium

metal and cadmium-109 stock solutions in volumetric flasks.

d. Procedure (Radioisotope Dilution) . To each of the

cells is added 3.00 ml of 0.1 F KN0~ followed by 1.00 ml of

109 cadmium solution containing Cd» These solutions were previously deaerated by passing prepurified nitrogen first through

a gas tower containing 0.1 F KN0~ and then through these solutions. Each cell was preelectrolyzed at -0.40 volts vs. S.C.E.

to remove traces of oxygen. Electrolysis was continued until

the residual current in each cell was identical. With the

165
cells in series, the control cell potential was held at -0.75

volts vs. S.C.E. and the time of electrolysis was either five

or ten minutes. Without interruption of the electrolysis,

samples of solution were simultaneously withdrawn from each

cell. Then 1.00 ml of each solution was accurately transferred

to a counting tube, placed in the automatic well counter and

counted, until 100,000 counts were accumulated.

e. Procedure (Current -integration). The same preelectrolysis procedure is carried out as described above. With

the cells in series and control cell potential at -0.75 volts

vs. S.C.E. , electrolysis is carried out to completion until the

residual current is reached. The potential control is then

immediately transferred to the sample cell where integration

of the current is recorded until the same value of residual

current as obtained in the control cell is reached. The time

of electrolysis in each case is about 35 minutes. The residual

current Is then integrated for the same length of time and its

contribution is subtracted from the entire integral. A similar

technique as described above appears in an article by Rechnitz

and Srinivasan [55 ].

3. Results and Discussion

Table 19 includes the data obtained by the radioisotope

method and that obtained by the current integration procedure.

Comparison of each technique at this concentration level leads

to the conclusion that the precision (expressed as standard

deviation of a single measurement) of the integration procedure is greater; however, the accuracy attained as shown in

the above table is comparable. It can also be said from this

study that for this concentration level, the accuracy of the

amount analyzed in the sample cell becomes greater as the

differential becomes smaller. The same conclusion was expressed

in a similar study [55]. Also represented are results obtained

at smaller concentrations.

In order to demonstrate the behavior of the sample cell

166
Table 19. Summary of the results of the determination

of Cadmium (II) in 0.1 M KN0

3

Radioisotope method

Control

cell(/zg)

Sample

cell(yug)

Found

mean (as)

% Rel.

error

a

°"s No. of

deter

200.05 400.19 396.33 -0.96 3.44 5

248.93 400.19 401.80 +0.40 3.15 5

323.16 400.19 399.22 -0.24 2.56 5

381.18 400.19 400.81 +0.16 2.39 6

19.02 38.51 38.35 -0.42 .71 6

22.92 38.51 38.29 -0.57 .60 6

26.71 38.51 38.58 +0.18 .79 7

30.53 38.51 38.27 -0.62 .44 5

2.15 4.25 4.15 -2.35 .11 5

2.15 2.97 3.01 +1.35 .20 5

Integration method

200.05 400.19 397.06 -0.78 1.25 6

248.93 400.19 397.45 -0.68 1.49 5

323.16 400.19 401.11 +0.23 0.76 4

381.18 400.19 400.69 +0.12 0.70

:ion of single measurement

6

3.

<r *= Standard deviat

167
cathode potential in the series arrangement, measurement of

the potential versus the S.C.E. was made while electrolysis

proceeded. In figure 581 is shown curves A, B, and C which

represent the potential as a function of time and as a function

of different ratios of sample to control cell concentrations.

It can be seen that the potential assumes the most cathodic

value immediately after electrolysis has begun and becomes

more anodic as electrolysis proceeds and finally reaches a

constant value. As the concentration in the sample cell approaches that in the control cell, the potential at the start

of the electrolysis approaches that of the controlled-potential

value. Thus, the trend observed indicates that the potential

will become more cathodic than the controlled-potential value

when the concentration in the sample cell falls below that in

the control cell. As was indicated in the introduction, this

should be prevented in order to exclude undesired electrode

reactions and thus allow the application of the substoichiometric principle.

4. Conclusion

The substoichiometric radioisotopic dilution principle has

been successfully applied to controlled-potential coulometry.

Further research in this area will be directed toward analysis

at the submicrogram concentration level. The factors affecting

the sensitivity will be evaluated and attempts made to minimize

them. Work in this direction is already in progress. The use

of an inert N« dry box should provide a minimum of oxygen interference while purification of the supporting electrolyte by preelectrolysis at controlled potential should greatly reduce

electroactive contaminants which affect the analysis. It Is

hoped that the high specific activity of many radioisotopes

will provide high sensitivity with this method.

(P. A. Pella)

168
-0.710

-0.700

-0.690

-0.680

-0.660

Jri -0.650

"J -0.640 —

-0.630

-0.610 —

-0.600

-0.590

-0.580

1 f l r i r

CONTROL CELL V vs S.C.E. o

.„,„ SAMPLE

RAT'° C0NTR0L

= 1.05 -0.74910

II II 1.24 -0.75120

A

„ 2.00 -0.74910

J I I I I I L

8 10 TlME(min)

12 14 16 18

Figure 58. Potential of sample cell vs. time

for various concentration ratios

169
D. Radioisotopic Dilution for Trace Chemical Analysis

1. Introduction

Two methods for trace elemental analysis have been developed.

One which was originated by Ruzicka and Stary [56 ] is called

substoichiometric radioisotopic dilution analysis, SRDA. The

SRDA method differs from classical radioisotopic dilution [57]

in that the same amount of material is isolated before and after

dilution, eliminating the need to measure the specific activity.

For some heterogeneous systems using a limiting amount of reagent, it is impossible to remove the same amount of element

before and after dilution; however, if the variables are controlled a graphical relationship can be obtained between the

amount of element present in the sample and the amount of diluted radioisotope that is separated. This method of analysis

is called the concentration dependent method (CDM). These

methods are related through the fundamental processes of chemical and isotopic exchange. By the application of the law of

mass action to the chemical process, and the subsequent application of the radioactivity balance relation it will be shown

that the relative radioactivity can be used in place of specific activity to measure the change in the initial concentration.

An inclusive theory has been developed and is partly described in this report. The theory of isotopic dilution analysis was reviewed by Alimarin [57] and the theory of SRDA was

developed by Ruzicka [56]. The CDM has been developed by the

present authors [58] and a theoretical treatment was developed

by Kyrs [59]. A theoretical approach which differs from

Ruzicka [56] and Kyrs [59] was developed. Also methods of

standard additions have been developed for the CDM and SRDA [1].

H. Wieler [60] and J. Rykeer [61] have developed theoretical treatment of the accuracy and precision of classical isotopic dilution analysis. The theoretical and practical considerations in SRDA have been considered along with a procedure to

minimize errors commonly arising in the application of the

method. The CDM has associated with it the common advantages

170
and disadvantages of methods which rely on calibration curves.

With respect to the sensitivity of the CDM and SRDA, the former

has been found to be more sensitive [1, pp 112-148, 58^ 59 ].

Ruzicka and Stary have reported an analysis for mercury and

zinc using SRDA [ 62,63]. Their procedure was reinvestigated

and some difficulties were found with the procedure for mercury.

Cadmium was determined in this laboratory [64] using substoichiometric amounts of dithizone for both model solutions and for a

zinc matrix where the cadmium was separated from interfering

elements by controlled-potential electrolysis.

The concentration dependent method has been used to extend

the sensitivity of the extraction procedures used to determine

mercury and cobalt [58], by using a limiting amount of EDTA in

an ion exchange separation. It has been found that the concentration dependent method could be applied to the adsorption of

traces of material on chromatographic paper impregnated with

manganese dioxide [1, pp 112-148].

The latter part of this report includes a summary of the

theoretical treatment of SRDA and CDM. An example of applying

the law of mass action to the radiochemical balance relationship

for the solvent extraction of mercury with dithizone and an

experimental procedure of verifying whether SRDA or CDM applies

will be explained. The results obtained in the analysis of

mercury and zinc along with a discussion of the precision,

accuracy and sensitivity of these methods are also summarized.

2. Highlights of the Theoretical Treatment of SRDA and CDM

SRDA, CDM, as well as classical isotopic dilution analysis

involve heterogeneous equilibria. It is necessary to transfer

mass from one phase to another and the substance isolated must

be in a pure form or isolated in a predictable manner. In order

to understand the methods. (SRDA and CDM), it is necessary to

apply the law of mass action to the heterogeneous equilibrium.

The fundamental expression is

aBj + bA = c C zl

+ dD (1)

171
where a, b, c, and d are the coefficients) B is the substance

to be analyzed, A is the limiting reagent, C is the complex

formed between A and B, and D is the ion replaced from B. The

signs are omitted for simplicity. The subscripts I and II refer to phase I and II. A and D may be in one phase or the

other, but B and C must be in different phases* The relationship

[C ]° [D] d

yg„ ,«

" [A] b

[ Bl ]* yf-^~

^^

(2)

applies for the above equilibrium.

The y

T s are the thermodynamic activities, K^g is £he thermodynamic constant , K?R

is the concentration quotient and T*- is

the activity quotient. 1\~ may assume unpredictable values and

in many cases is not known. If we can assume Lg to be unity

then K« B

is equal to K^. It is a simple matter using these

assumptions to calculate m, the mass isolated of the element of

interest before and after dilution.

This amount, m, can be related to the radioactivities isolated through the radioactivity mass balance relation. The

radioactivity mass balance relation generally takes the form

(x + Y)i=iy. (3) m« m*

where X is the unknown weight of the element, and Y is the

known total elemental weight of the radioisotope. The specific

1 activity of the radioisotope before dilution is A, = -—, and

o

^* A« - —— is the resultant specific activity after dilution,

where a-, and a« are the activities in counts per minute for a

reproducible counting geometry which corresponds to weight nu

and nu of the element before and after dilution, respectively.

SRDA requires that equal amounts are Isolated before and

after dilution through the use of a substoichiometric amount

of reagent. This requires a high KTM- for the reaction. If

172
99.9% of the reagent is used up then nu = iru for all practical

purposes. It is evident from equilibrium considerations that

nu can never exactly equal iru. If the equilibrium constant is

low, 99.9% of the reagent is not consumed before and after

dilution, and the amount isolated is not independent of the

initial concentration. Using the proper amount of limiting

reagent and appropriate experimental conditions, the assumption

that equal amounts are isolated before and after dilution is

valid for a number of systems. Then the following relation

(X + Y) &2 ~ Yai (equation 4) can be used. The method only

requires the measurement of the radioactivities (a-, and a«)

and a knowledge of Y.

The CDM is based on the distribution of the elemental

species between two phases as a function of the initial concentration. In the concentration dependent method the amount

isolated is dependent on the initial concentration. This

process must be combined with the process of specific activity

change. For any given series of experiments a-. , Y, and nu are

constants; a

2 ...., X^.*.., nu...., are variables; a,, a2»»*^

are determinable experimentally, but nu and X cannot both be

determined from the radioactive material balance relation.

The total initial concentration C. is equal to X plus Y. If

a

l

one lets —- Y = K T it can be shown that K» = &.. the total

m.j t

activity in the system. From the radioactivity material balance relation a^C, = a.nu (equation 6). It is possible to

calculate nu for various values of C

fc using the law of mass

action and assuming values for the total radioactivity, (a

fc

, added to the system); it is a simple matter to calculate a2 , the radioactivity isolated. A plot of radioactivity isolated

versus initial concentration can be obtained. The CDM is valid

if the amount isolated before and after dilution is not constant but varies as a function of the initial concentration.

173
3. An Example of Applying the Law of Mass Action to the

Radioactivity Mass Balance Relation

Ruzicka [56] assumed that 99.97o of the organic reagent is

used in the reaction of interest • It is more useful not to

make this assumption because it allows us to determine whether

SRDA or CDM method applies. An example will be illustrated for

the solvent extraction of mercury with substoichiometric amounts

of dithizone. The solvent extraction of mercury with dithizone

can be represented by the equation

H S

++

(aq)

+ 2H

2

Dlz

o

= H S<HDl2>2 + 2H

(aq) (7)

This equation does not take into consideration the side reac,--

tions of mercury or dithizone. For a more complete treatment

of the equilibria see Sandell [65] and Ringbom [66]*

= a constant for a given series of experiments

* amount of mercury initially present in grams

= amount of mercury dithizonate formed in

grams

= volume of the organic phase in milliliters

= volume of aqueous phase in milliliters

initial concentration of dithizone, in moles/

liter

Let [H

+

]

X

m

diz

at.wt.= atomic weight of mercury

[Hg(HDiz)

2

] [H

+

]

2

K — A

K -

[Hg] [H

2

E

r m

at . wt

.

1000 [H

+

]

2

F

X - m

V at. wl

- — 1000

_ CDi

2m

at . wt

.

V

o

1000

2

(8)

(9)

Since K, V , [H ], X, V and CD. are known, m can be readily

solved for any series of experiments for the X. value of X (where

i denotes initial concentration). If m is relatively constant

then SRDA is valid and if m varies, then from knowing m, a. , and

c tthe radioactivity one expects to isolate can be calculated

174
from equation 6. Using these relationships for the above

example, SRDA was shown to apply.

This treatment is not completely valid since the amount of

mercury present should be corrected for the formation of hydroxo

complexes, ( Hg°H)Taa ) and H&(°H

)2(aa) and f°r the solubility

of

mercury dithizonate at low concentrations in the aqueous phase.

The solubility of dithizone in water has not been taken into

account and a correction for this may be needed for low concentrations of dithizone. These corrections can be approximated

[65 ,66].

4. An Experimental Procedure to Distinguish between SRDA

and CDM

From the radioactive material balance relation (equation 3)

a-, y

it can be shown that when SRDA applies, —=• = «• + 1 (equation 10),

a« i a plot of the ratio of radioactivities versus the amount X

should give a straight line with a slope of 1/Y and an intercept

of 1. But if the SRDA principle does not apply, a curve which

is still analytically useful can be obtained. When m^ i m

2

then from the radioactivity material balance relation,

[ijK x [r\ + mi (I1)

is obtained, where itu can be calculated from the law of mass

action, and it is possible to obtain a straight line from the

T

a

ll data. Let —- nu = Z. A plot of Z versus X should give a slope

m

l

2

of y— and an intercept m,

.

5. Experimental

The procedure developed by Ruzicka was used to determine

mercury [62] and zinc [63] with the following exceptions: the

concentration of dithizone (see tables 20 and 21) and the specific activity of radioisotopes used was different. The

specific activity of mercury-203 was 458 mCi/g and the specific

activity of zinc-65 was 1784 mCi/g.

175
Table 20L Results obtained with zinc

Amount

added

Amount

found Standard3

deviation

% dev

.

from

added

value

Concen

diz(M)

No. of

deter

1.000 0.983 ± 0.005 -1.7 lxlO"4

5

0.100 0.1030 ± 0.0056 +3.00 5xl0"5

5

0.0010 0.0010 ± 0.00008 +1.0 2xl0" 6

5

a Of a single determination,

Amount

added

ffg/ml

1.00

0.100

0.0100

0.00100

Table 21. Determination of Mercury

Amount

found

1.02 ± 0.02

0.100 ± 0.002

0.0131 ± 0.0004

0.00072 ± 0.0002

Rel

stda

dev %

% dev

from

added

value

Concen

diz(M)

No. of

deter

1.7 + 2.00 2xl0" 5

8

2.0 < 1.00 lxlO"5

6

3.3 +31.0 2xl0" 65

2.7 -28.0 lxlO" 65

Of a single determination.

176
6. Discussion

The graphical procedure was used to determine whether CDM

or SRDA was applicable. The advantage of this approach is that

it allows one to bracket the sample, and the curve can be used

when the SRDA formula does not apply. Also the amount in the

tracer need not be known and it is evident that the total

elemental concentration of the tracer can be determined through

the use of this approach. Also, when the amount in the tracer

is small or well known one can apply a method of standard additions.

The way Ruzicka and Stary calculated the error associated

with the analysis appears to be biased since they assumed no

error is associated with the radioactivity isolated before

dilution in the determination of mercury, and they paired the

activities a-., a^ to obtain the most favorable results in the

determination of zinc.

The data obtained in this laboratory for zinc have good

precision and accuracy (see table 20). The data obtained for

the determination of mercury is reported in table 21 The

precision is acceptable by normal analytical standards, but

the accuracy is poor at the 0.01 and 0.001 Ag/ml levels. The

accuracy can be corrected to within 4% of the added value by

the use of a calibration curve which allows the sample to be

bracketed.

The interrelationship between accuracy and precision varies

in different ways for the different analytical methods. A

detailed error analysis has been performed to conclusively

demonstrate that for SRDA the accuracy and precision are inversely related, i.e., as one increases the other decreases.

Ways of overcoming this paradox have been developed.

The precision and accuracy of the method can be affected

by a number of factors. The most serious errors affecting the

precision in solvent extraction are caused by the evaporation

of the organic phase and oxidation of the dithizone. It is

evident at the submicrogram level that contamination due to

177
reagents, apparatus and airborne contamination may affect the

accuracy as well as the precision. The matrix may have a profound effect upon the accuracy of the method. If pre concentration is necessary, losses may occur and the blank is increased.

It is possible through the use of tracers to correct for losses.

The blank can be corrected for by a method of standard additions [1, pp 112-148). Interferences from the matrix can also

be corrected by a method of internal standards or by using masking agents [1, pp 112-148]. When m.. i nu the graphical approach

can be used to bracket the sample and the amount (Y) need not

be known when calibration curves are used.

The blank and specific activity of the radioisotope are

the two most important factors limiting sensitivity. The

sensitivity of the method can be extended by the use of micro

methods, methods of preconcentration, and a clean environment.

An attempt has been made to verify the concept of radioisotopic dilution techniques for tracer elemental analysis.

Considerable effort has been expanded in demonstrating the

precision, accuracy, and sensitivity of these methods, and a

more detailed report of this work will be made in the near

future.

(A. R. Landgrebe and L. T. McClendon)

E. Publications

Determination of Trace Amounts of Cadmium and Silver by

Substoichiometric Radioisotopic Dilution Analysis.

A. R. Landgrebe, J. R. DeVoe and L. T. McClendon, Trans.

Am. Nucl. Soc, 8, 315-316, 1965.

F. Consultations

George Welford, Health and Safety Laboratory,

Atomic Energy Commission, New York, New York

Emilio J. Trioanelb, Northeastern Radiological Health Lab.

109 Holton Street, Winchester, Massachusetts

178
6. LIST OF TALKS

1. A. R. Landgrebe , "Radiochromatographic Methods",

American Chemical Society, Atlantic City, September 1965.

2. J . J . Spi jkerman , A. R. Landgrebe , F. C. Ruegg and

J. R. DeVoe, "The Use of MBssbauer Effect to Study the Adsorption of Iron on Cationic Exchange Resin"; , American Chemical

Society, Atlantic City, September 1965.

3. J. J. Spi jkerman, A. R. Landgrebe and F. C. Ruegg,

MBssbauer Effect in Ethylenediaminetetraacetatoiron (III) Complexes", American Chemical Society, Atlantic City, September

1965.

4. A. R. Landgrebe , L. T. McClendon, and J. R. DeVoe

,

"A New Method of Analysis Using Radioisotopic Tracers - A

Concentration Dependent Method", American Chemical Society,

Atlantic City, September 1965.

5. P. A. Pella, A. R. Landgrebe, J. R. DeVoe and W. C.

Purdy, "Differential Controlled-Potential Coulometry Utilizing

Radioisotopes", American Chemical Society, Atlantic City,

September 1965.

6. F. C. Ruegg, J.J. Spi jkerman , and J. R. DeVoe, "A

MBssbauer Spectrometer for the Structural Analysis of Materials"

IAEA, Warsaw, October 1965.

7. J. R. DeVoe , "Applications of MBssbauer Spectrometry

to Chemical Analysis", American Chemical Society, Central Ohio

Valley Section, Marshall University, Huntington, West Virginia,

November 1965.

8. J. R. DeVoe , "Applications of MBssbauer Spectrometry

to Chemical Analysis" , American Chemical Society, Louisville

Section, Bellarmine College, Kentucky, November 1965.

9. J. R. DeVoe , "The Radiochemical Analysis Program at

the National Bureau of Standards", American Chemical Society,

Indiana -Kentucky Border Section, Evansville, November 1965.

10. A. R. Landgrebe , " Subs toichiome trie Radioisotopic

Dilution Analysis of Silver and Cadmium" , American Nuclear

Society, Washington, D. C. , November 1965.

11. A. R. Landgrebe , L. T. McClendon, and J. R. DeVoe,

"A New Method of Analysis Using Radioisotopic Tracers - A

Concentration Dependent Method", Eastern Analytical Symposium

and Instrument Exhibit, New York, November 1965.

179
12. F. C. Ruegg , "Absolute Velocity MBssbauer Spectrometer",

American Nuclear Society, Washington, D. C. , November 1965.

13. J. J. Spijkerman and F. C. Ruegg , "Determination of

Coordination Numbers for Iron Chemistry", New England Nuclear

and Technical Measurement Corporation, joint sponsors, N. Y.

,

January 1966.

14. D. K. Snediker , "The MBssbauer Effect of Sn119m in

Pd-rich Palladium-Tin Solid Solutions and the Intermetallic

PdSn" , New England Nuclear and Technical Measurement Corp.,

joint sponsors, N. Y. , January 1966.

15. A. R. Landgrebe

,

"A Critical Evaluation of the Method

of Subs toichiome trie Radioisotopic Dilution Analysis",

Pittsburgh Conference on Analytical Chemistry and Applied

Spectroscopy, Pittsburgh, February 1966.

16. J. R. DeVoe , "Activation Analysis on Nuclear Resonance

Fluorescence Spectroscopy" , Nuclear Science and Engineering

Seminar, Catholic University, Washington, D. C. , May 1966.

17. J . J . Sp i j kerman , "Standard for Chemical Shift of

Iron Compounds in MBssbauer Spectroscopy" , Society for Applied

Spectroscopy, Chicago, June 1966.

18. L. May and J. J. Spijkerman, "A Study of Iron Coordination Chemistry by MBssbauer Spectroscopy", Society for

Applied Spectroscopy, Chicago, June 1966.

19. L. A. Currie , "Systematic Errors in Recovery and

Detection Efficiency as Related to Radiochemical Analysis"

,

BioAssay and Analytical Chemistry Conference, Albuquerque,

October 1965.

180
7 . PERSONNEL

Radiochemical Analysis and Activation Analysis,

J. R. DeVoe, Section Chief

Activation Analysis

E. D. Anderson

D. A. Becker

B. S. Carpenter

W. D. Kinard

F. A. Lundgren

G. J. Lutz

S. S. Nargolwalla

W. P. Reed

G. L. Rhinehart - Terminated

R. R. Ruch

G. W. Smith

W. Jester - Summer student, 1965

M. R. Crambes - Guest Worker (6 months on NATO Fellowship

and 1 year Contract) Atomic Energy Establishment of Grenoble, France

Instrumentation

W. N. Bettum

R. W. Shideler

P. N. Thomas

Nuclear Chemistry

L. A. Currie

Radiation Techniques

W. L. O'Neal

F. C. Ruegg

D. K. Snediker

J. J. Spijkerman

E. A. Rhodes - Summer student, 1965

M. G. Hollstein - 1 year contract - Karlsruhe Center of

the German Atomic Energy Establishment

Radioisotope Tracer Techniques

T. E. Gills

A. R. Landgrebe

L. T. McClendon

P. A. Pella

181
8. ACKNOWLEDGMENTS

The Activation Analysis and Radiochemical Analysis Sections

wish to thank Dr. J. Elliot, Dr. Keith Marlow, Mr. E. Nowstrop,

Mr, E. Bebbs, Mr. L. Harris, and Mr. R. Vogt of the Naval

Research Laboratory Reactor Facility for making the irradiation

of samples possible. In addition, we wish to thank the NRL

Metallurgy Division, which has assisted several times in the

procurement of reliable, pure elemental standards for our work

in neutron activation analysis. We also wish to acknowledge

the assistance of the NBS Health Physics staff who have helped

us with the safe handling of these samples.

We wish to express our thanks to Dr. C. 0. Muehlhause and

his staff for their cooperation in making arrangements for our

use of the new facilities in the NBS Reactor Building. Further,

the assistance of Dr. H. W. Koch, Dr. J. E. Leiss and staff of

the Radiation Physics Division for arrangements to use the

LINAC facilities is acknowledged. The assistance of Mr. Goetz,

Acting Chief, as well as Mr. H. J. Rouse, Mr. T. B. McKneely,

Jr., and Mr. M. F. Kelly of the Plant Division, NBS, is also

acknowledged. We wish to thank Dr. J. Cameron and his staff

for assistance in statistical analysis of experimental data

.

These sections acknowledge Mrs. R. S. Maddock for her

assistance in preparing this report.

Special appreciation is expressed to Mrs. M. Fenstermaker

and Mrs. V. Durkay who typed the entire report and whose tireless efforts as section secretaries have made our entire

operation more efficient and effective.

182
9. LIST OF REFERENCES

[1] DeVoe, J. R. , editor, NBS Technical Note 276 (1965)

[2] Muehlhause, C. 0., editor, NBS Report 8998 (1966)

[3] Sheely, W. F. , NBS Report 9081 (1966)

[4] Anders, 0. U. and Briden, D. W. , Anal. Chem. 36, 287 (1964)

[5] Robinson, Berol L. , "Precision Determination of Gamma Ray

Energies with the Scintillation Spectrometer." G. D.

T Kelly, editor, Proceedings of a Symposium on Applications

of Computers to Nuclear and Radiochemistry, Gatlinburg,

Tenn., Oct. 1962, NAS-NS-3107, 67-73.

[6] Cumming, J. B. , "CLSQ, The Brookhaven Decay Curve Analysis

Program," G. D. O'Kelley, editor, Proceedings of a Symposium on Applications of Computers to Nuclear and Radiochemistry, Gatlinburg, Tenn., Oct. 1962, NAS-NS- 3107 , 25-33

[7] Brown, E. , Hague, J. L. , and Bright, H. A., J. Research,

NBS 47, 380 (1951).

[8] "Experimental Statistics)' Mary G. Natrella, editor, NBS

Handbook 91 (1963)

[9] Table of Isotopes, Strominger, Hollander, and Seaborg,

Rev. Mod. Phys.7 30, No. 2(11) (1958).

[10] Hughes, D. J. and Schwartz, R. B. , "Neutron Cross Sections,"

BNL-325 (1958) 2nd Ed.

[11] Ibid, Supplement No. 1, Jan. 1960.

[12] Macklin, R. L. and Pomerance, H. S. , "Progress in Nuclear

Energy-I", McGraw-Hill, New York (1956) p 180.

[13] Yule, H. P., Anal. Chem. 37, No. 1, 129-132 (1965).

[14] Bowen, H. J. M. and Gibbons, D. , "Radioactivation Analysis,"

Oxford University Press, Cambridge, U.K. (1963) p 98.

[15] Hoste, J., Pure and Applied Chemistry, 1, 99 (1960).

[16] Leliaert, G., Hoste, J., and Eeckhaut, J., Anal. Chim.

Acta, 19, 100 (1958).

[17] Hoste. J., Bouten, F. , and Adams, F. , Nucleonics 19, 118

(1961).

183
[18] Berlandi, F. J., and Mark, H. B. , Jr., Chem. Eng. News,

p 84 (Sept. 1964).

[19] Mark, H. B. , Jr., and Berlandi, F. J., Anal. Chem. 36>

2062 (1964).

[20] Mark, H. B. , Jr., Berlandi, F. J., Vassos, B. H. and

Neal, T. E. , "Proceedings of the 1965 International

Conference: Modern Trends in Activation Analysis,"

Texas A & M Univ., College Station, Texas.

[21] Vassos, B. H. , Berlandi, F. J., Neal, T. E. , and Mark,

H. B., Jr., Anal. Chem. 37, 1653 (1965).

[22] General Electric Chart of the Nuclides, March 1965 ed.

[23] Heath, R. L. , Phillips Petroleum Report, IDO-16408 (1957).

[24] DeVoe, J. R., Kim, C. K. and Meinke, W. W. , Talanta 3,

298 (1960).

[25] DeVoe, J. R. , Nass, H. W. and Meinke, W. W. , Anal. Chem.

33, 1713 (1961).

[26] Silker, W. B., Anal. Chem. 33,233 (1961).

[27] Ruch, R. R. , DeVoe, J. R. , and Meinke, W. W. , Talanta 9,

33 (1962).

[28] Qureshi, I. H. and Meinke, W. W. , Talanta 10, 737 (1963).

[29] Orbe, F. E., Qureshi. I. H. , and Meinke, W. W. , Anal.

Chem. 35, 1436 (1963).

[30] Qureshi, I. H. , and Meinke, W. W. , Radiochimica Acta 2,

99 (1963).

[31] Kim, C. K. , and Silverman, J., Anal. Chem. 37, 1616 (1965),

[32] Qureshi, I. H. , personal communication.

[33] Jangg, G. , Metall 16, 639 (1962).

[34] Dyer, F. F. and Leddicotte, G. W. , "The Radiochemistry

of Copper," NAS-NS 3027 (1961).

[35] Duncan, J. F. and Oakley, B. W. , J. Chem. Soc. 1955,

1401 (1955).

[36] Latimer, W. M. , "Oxidation Potentials," Prentice-Hall,

Inc., Englewood Cliffs, N. J., (1961).

184
[37

[38:

[39:

[4o;

[41:

[42

[43:

[46:

[47:

[48:

[49:

[so;

[51:

[52

[53:

DeVoe, J. R. , editor, NBS Technical Note 248 (1964).

Shideler, R. W. , "Proceedings of the 1965 International

Conference: Modern Trends in Activation Analysis," Texas

A & M Univ., College Station, Texas.

Hill, R. L. NBS Technical Note 168 (1963).

Engelkemeir. D. , Rev. Sci. Instr. , 227 (No. 8) 589

(1956).

Spijkerman, J. J., Ruegg, F. C. , DeVoe, J. R. . Snediker,

D. K. , O'Neal, W. L. , NBS Technical Note 260-13, to be

published.

Walker, L. R. , Wertheim, G. K. and Jaccarino, V., Phys.

Rev. Letters, 6, 98 (1961).

Snediker, D. K. , "The MBssbauer Effect of Sn ' in

Palladium-Rich Palladium-Tin Solid Solutions," MBssbauer

Effect Methodology, Vol. 2_, Plenum Press, New York, In

press.

Ruegg, F. C, Spijkerman, J. J., and DeVoe, J. R. , Rev.

Sci. Instr., 36, 356 (1965).

Herber, R. W. , and Spijkerman, J. J., J. Chem. Phys. 43,

4057 (1963). ~~

Hill, R. L. , NBS Technical Note 168 (1963).

Seller, H. , Helv. Chim. Acta 46, 2629-2635 (1963).

Pollard, et al, Anal. Chim. Acta 14, 70 (1956); J. Chem.

Soc, 466 (1951); J. Chem. Soc. , Z70 (1951); Nature 163 , 292 (1949); J. Chromatog. 2, 282 (1959).

Van Erkelens, P. C. , Nature 172, 357-8 (1953).

Van Erkelens, P. C. , Anal. Chim. Acta 25, 570-578 (1961).

Welford, G. A., Chiotes, E. L. and Morse, R. E., Anal.

Chem. 36, 2350 (1964).

Hais, I. M. , and Macek, K. , Paper Chromatography, Academic

Press, N. Y. (1963).

Stahl, E., editor, Thin Layer Chromatography: Ch. M.

,

Thin Layer Chromatography of Inorganic Ions by A. Seller;

Ch. N. , Spray Reagents for Thin Layer Chromatography by

D. Waldi, Academic Press, Inc., N.Y. (1965).

185
[54] Connally, R. E. and Scott, F. A., "Hanford Controlled

Potential Coulometer , " AEC Report HW-65919 (1960).

[55] Rechnltz, G. A. and Srinlvasan, K. , Anal. Chem. 36, 2417

(1964).

~~"

[56] Ruzicka, J. and Stary, J., Talanta 8, 228-234 (1961).

[57] Alimarin, I. P. and Bilimavith, G. H. , Int. J. Appl. Rad.

Isotopes ]_, 169 (1960).

[58] Landgrebe, A. R. , McClendon, L. T. , and DeVoe, J. R.

,

Radiochemical Methods of Analysis, Vol. II, Inter. Atomic

Energy Agency, Vienna, 321-333 (1965).

[59] Kyrs, M. , Anal. Chim. Acta 33, 245-256 (1965).

[60] Weiler, H. , Int. J. Appl. Rad. Isotopes 12, 49-52 (1961).

[61] Rykheer, J. and Bozalek, S. , Application of Isotopes and

Radiation, Vol. II, National Conf. on Nuclear Energy,

Pretoria, Republic of South Africa, 72-82 (1963).

[62] Ruzicka, J. and Stary, J., Talanta 8, 535-38 (1961).

[63] Ibid. 8, 296-300 (1961).

[64] Landgrebe, A. R. , DeVoe, J. R. , McClendon, L. T., Trans.

Am. Nuc. Soc. 8, 315-316 (1965).

[65] Kolthoff, I. M. , Treatise on Analytical Chemistry, Pt. 1,

I, Ch. 14, Complexation Reactions by Anders Ringbom, The

Interscience Encyclopedia, Inc., N. Y.

[66] Sandell, E. B. , Colorimetric Determination of Traces of

Metals, Interscience Publishers, Inc., N. Y. (1959)

pp 139-174.

186
APPENDIX I

NOTES ON THE USE OF THE G.E. TIME -SHARING COMPUTER

FOR MULTICOMPONENT DECAY CURVE ANALYSIS

A, Introduction

Principles, method of use, interpretation, and illustrations of decay curve analysis will be presented below. The

specific program referred to is "CLSQ-1". This program is a

modification of "CLSQ" which was written by G. Lutzj "CLSQH,

in turn, was prepared (in part) by translation of the original

"CLSQ" (Fortran) of J. Cumming [Al] into BASIC. "CLSQ-1" takes

observed numbers of counts, counting times, counting intervals,

and half-lives, and it calculates initial counting rates with

their standard deviations for data which may be treated by

simultaneous equations or, if overdetermined , by least squares.

In the case of least squares, the output also includes the

RATIO of the observed deviation to the standard deviation for

each point, and also the quantity, FIT, is calculated. The

on-line feature allows convenient changes of model, elimination of negligible components, rejection of outliers, and

evaluation of "true" observation variance.

B. Mathematics

1. Least-Squares Formulation

Observed counting -rates, Y., at observation (mid-) times,

t., are related to the initial rates of the components, x^, by

the matrix equation:

A | x > =

| y >

or EAjlj Xj = y±

(1)

where k

±

- e" A

J

fc i

Applying the criterion of minimum variance ("least -squares")

one reduces equation (1) to a set of simultaneous equations:

(2) B | x = |z>

where

i

B, . = y A., A. .w, = B ., i ik ij i jk

187
*k

= ^ yiAikwi

w, being the "weight" attached to the ,th observation.

Inversion of the B-matrix yields the solution for | x>,

x> = B"1Bfx>"= B~X |z> (3)

°r X

j = ?

(B

" 1)

jkzk

The variance for x. is given by the product,

•J 23 / calc\2

.-* ,,-ix i wi

( yi-y i} ,,, *. - (B )

J3

(4)

where v = (no, observations)- (no. unknowns) = no. degrees of

freedom

2. Weights, w.

Two cases may be considered,

(a) equal weights, w. = 1

(b) unequal weights, w. = 1/°.

If equal weights are assumed, the second factor on the

right-hand side of equation (4) is just equal to s , the sample

variance , and , therefore

,

'i-KB-V1'2 -.

If weights are derived from counting statistics, the second

2 factor referred to above is equal to (s/a ) , and "in the long

run" it has a mean value of unity. Thus, if observations are

properly weighted according to their reciprocal variances, the

-1 1/2 standard errors are numerically equal to [ (B ) . . ] . CLSQ-1, as written, expresses weights as in case (b) , above,

and includes variance contributions from sample counting,

background standard deviation, and "external" (or additional)

variance. One may set all weights equal to unity, if desired,

by typing:

140 LET W(R) = 1

188
In this case, however, the standard errors of the results are

given by Equation (4) , and must be calculated from the product

of the output data: "SIGMA" and "FIT", which are equal to

1 1/2

[ (B )..] and s, respectively. "FIT" no longer has its previous meaning - that of indicating consistency between s and a

3. "FIT"

FIT is a measure of the consistency of the observed deviations with those expected from counting statistics. It is

2 1/2 2 defined as [x / v ] , where x / v serves as an estimate of

o (s/cr ) , and in the long run, Is expected to have the value,

unity. Thus, v • (FIT) 2 follows the x

2

- distribution for v - degrees of freedom. For large v

, (FIT/ ~ X / v. , is approximately normal, with a mean of unity and a variance of 2/v

"FIT" is calculated according to equation (5).

(5)

4.

(FIT) 2 = 1

V i

calcs2

L" yi

; a ±

2

"RATIO"

(RATIO)

£ . W-y±

calc

) (6)

"RATIO" thus gives a measure of each deviation in terms of

its corresponding standard deviation. This quantity (RATIO)

should be approximately normal with a mean of zero and a variance of unity.

C. Use of CLSQ-1

1. Normal Use

a. Input Data . The READ statements are shown in the

first part of the program (attached) , and a sample of such

input data Is included in example la. Meanings of the symbols

follow:

189
N = number of observations

P = number of components (unknowns)

B - background rate (cpm)

S9 = standard deviation of background (cpm)

F = "external" fractional standard deviation, i.e.,

remaining relative standard deviation, if that

due to counting statistics were equal to zero.

(Generally, F may be set equal to 0, or 0.01, if

desired).

T(0),M(0) = initial ("zero") time - hours, minutes, respectively. [D(0) - days- assumed to be zero]

T(R),M(R) = time of the start of the R— observation - hours,

minutes - respectively.

U(R) = time interval for R— observation (min)

Y(R) = number of counts accumulated during the R

observation.

H(J) - half-life (min) for component, J.

b. Output

1) For simultaneous equations and least-squares

analyses, the following information is "put-out", for each

component

component (index) number

half-life (min)

initial (zero-time) counting rate (cpm)

standard error of initial rate (cpm)

2) For least-squares analyses, only, the following

additional data are typed:

T(R), mid-time for observation, R

Y(R) , net rate (cpm) for observation, R

Y-CALC(R), net rate (cpm) for observation, R,

based upon the calculated curve . RATIO(R), ratio of observed deviation to standard

deviation, as defined in equation (6).

2 1/2 FIT, ( X /v) ' - a measure of goodness-of-fit , as

de fined in equati on ( 5 ) .

190
2. Modifications

a. Dead-time Correction . Should it become necessary

to correct for dead-time losses, one may include statements

113 , 114 , and 161 , as shown with the first part of the program

(attached) • (T = dead-time in [is.)

b. D(R), T(R), M(R), U(R) , Y(R) . The above quantities

have been given separate ,T READTr statements (No. 130 through ( No. 134 ) so that one or more may be given fixed values. For

example, if all observations take place on the same day, one

might type

:

130 LET D(R) = If all starting times are initially given in minutes, one

would type:

130 LET D(R) = 131 LET T(R) = (Cf. examples: 1, 2, and 3)

One could express time in any other units, if desired, setting

D(R) and T(R) to 0, as above, and making sure that M(R) , U(R),

B, S9, M(0), and H(J) all have consistent units of time . (For

example, all might be expressed in days or counts per day;

counts per fortnight, etc.)

If the time intervals, U(R) , or numbers of counts, Y(R) , are

fixed, such fixed values might be inserted:

133 LET U(R) = 10

or 134 LET Y(R) = 2500

If a simple counting program is followed - as with a multichannel scaler, one might replace 132 with a statement such as,

132 LET M(R) = 65* (R-l)

c. "Internal" Background . As with the GEM-program, [A2]

long-lived components and background may be treated tegether

as a single component, especially if interest is primarily in

a shorter-lived component. Greater accuracy may be achieved

in this way, if a long-lived component might otherwise be

ignored. If all components are properly included in the first

191
place, however, the precision is better if the observed background is subtracted in the normal fashion. (A component is

"long-lived" in the above sense if its decay during the time

period covered by the set of observations is small compared to

the standard deviations of such observations. Thus, typically,

a component having a half-life greater than about 100 times

the total time interval of observation may be considered "longlived.')

d. Trouble -Shooting . Perhaps the most significant

aspect of the on-line approach is the possibility of rapid data

or model changes following the output of previous calculations.

Discussion of appropriate types of change will be dealt with

below, but here it will be useful to summarize the "mechanics"

of such changes.

First, as is probably obvious, one may readily alter or

eliminate input data simply by retyping the appropriate input

statement. Second, since the significance of changes are seen

principally in "RATIO", "FIT", and the calculated initial rates

and their standard errors, needless time and space are consumed

in retyping the mid-times, "observed" net rates, and "calculated"

net rates for each observation. Hence, instructions are given

at the beginning of the program in REM f s 2-5 to alter the program so as to eliminate the unnecessary steps during troubleshooting.

D. Interpretat ion

1. Indicators of Trouble

a. Large negative results . If the result for a given

component is negative by an amount significantly greater than

its associated standard error there is something wrong with the

input information. Since the results may be interpreted (generally) using the normal distribution, one may specify levels

of confidence with which such negative results may occur.

Using one-sided confidence intervals we reach the following

conclusions

192
Result Probability of Occurring by Chance

< -lo 15.87%

< -2 a 2.28%

< -3 a 0.13%

Thus, a result more negative than -2 o suggests difficulty.

b. FIT . ("FIT") 2

, which follows the x

2

/ v -distribu2

' tion, and is an estimate of (s/ a ) , would be expected to

approach unity with increasing N. Acceptable limits for "FIT"

vary with N, and a few such limits are given below.

95% Confidence Interval*

y = N- P Lower Limit Upper Limit

1 0.031 2.24

5 0.407 1.60

10 0.569 1.43

20 0.692 1.30

100 0.860 1.14

Values smaller than the lower limit are only apt

to arise from too large an "external" standard

deviation, F, whereas values which are too large

may arise from several sources, discussed subsequently; the great advantage is that one may

quickly be alerted to trouble by examining "FIT".

c. RATIO , The individual "RATIO'S" provide a means

for spotting specific sources of trouble, rather than just

being general indicators - like the two above. As with the

indicator, FIT, however, RATIO is not available for simultaneous equations, but only for least-squares analyses.

Limits for the magnitude of "RATIO" may be deduced from the

binomial and normal distributions. If one were to examine but

one RATIO, upper and lower confidence limits could be deduced

from the normal distribution, that is, the 95% confidence

2 1/2 The limits stated are those for "FIT" or (x /„ ) , they correspond ipond to the two-sided 95% confidence interval for (FIT)*

or x 2 /v . 193
interval would extend from -1.96 to +1.96. In examining a set

of N-RATIO f s, however, one must apply also the binomial distribution,

W( >'l) = 1 - W(0) = 1 - (1 - a) N

or a - 1 - [1 - W(> 1)] 1/N (7)

where, W(^l) = probability that one or more RATIO will fall

outside the prescribed limits, by chance.

a - corresponding level of significance for the

normal distribution

(Thus, for N = 1, a = W( £1).)

Intervals based uppn equation (7) are given below, for the

case, W( - 1) = 0.05. (Note: Application of the Chauvenet

criterion would not be a correct procedure.)

N Limits for RATIO

1 ± 1.96

5 ± 2.57

10 ± 2.80

20 ± 3.00

50 ± 3.27

If an occasional value of RATIO lies outside the above

limits, it might be considered an outlier, and treated accordingly. If a large portion of the RATI0 T s exceed the limits,

then very likely something is wrong with the model or the

assumed standard deviations (of the individual observations)

.

Another way in which RATIO 1 s may be helpful is in indicating trends. That is, if a number of consecutive values are

positive or negative, and especially if they proceed from

positive to negative or vice versa, one may suspect that the

"model" half-life is too long or too short, respectively.

These effects are illustrated clearly in example lb.

2. Sources of Trouble

a. Outliers . An outlier may most readily be detected

by examination of the RATIO T s. Although it may also affect the

other "indicators "

f its effect on a specific ratio should be

194
most obvious, since one such ratio should show a deviation

much greater than the others. If such is the case, one may

eliminate the corresponding datum and reprocess the remaining

data. It is unwise, however, to reject more than one or two

points; if several of the RATIO f s lie outside the limits given

above, very likely another source of difficulty is at fault.

b. Additional (non-counting-statistics) Variance . i If

additional random errors are operating (e.g. positioning reproducibility, temperature fluctuations, etc.), but are not included in the weighting, the weights will be too great (a. *s too

small), and all three indicators may suggest trouble. This

source of trouble may be likely if the RATIO'S take on a range

of values, whose magnitude is too large, but in which positive

and negative values are more or less randomly interspersed.

The solution to the difficulty is to insert a value for F, the

extra relative standard deviation, such that FIT, on the aver- age , is equal to unity. Such a value for F, however, should be

reasonable in terms of expected or experienced performance,

and other difficulties should not be indicated after this has

been done. Perhaps a reasonable value for F, in most counting

experiments, is about 0.01.

c. Incorrect Model . If components are missing from

the model, or if incorrect half-lives have been used, all

three indicators may be affected. This source of trouble is

perhaps the most likely one, and it may be studied by examining

the RATIO r s for trends, as suggested above, and by testing the

data using various reasonable models. In general, models including components which are really absent will give no trouble,

except that standard errors will be larger because of the

"more complicated" analysis.

d. General Comments

1) As stated earlier, the most convenient method

for exploring the trouble sources discussed above, is to eliminate unnecessary parts of the program and output, as directed

in REM's 2-5.

195
2) In the case of a poor FIT, a major component

may be approximately estimated by the calculated result together with a standard error equal to:

[(B" I

) i

. • s 2

]

1 /2 = "SIGMA" • "FIT"

This is rigorously correct for equal weights, even though the

weight be unknown, and is "expected" to give "safe" results

even in the case of imperfect models or data. (This last

suggestion comes from the paper by Nicholson et al. [A2].)

3) Elimination of "Undetectable" Components * If

a component is undetectable in the sense that its standard

error is comparable to or larger than the absolute value of

its calculated (initial) rate, then one may consider eliminating

such a component from the model. This will have the effect of

"improving" (making smaller) standard errors of remaining components. Thus, if the hypothesis that certain ("undetectable")

components are absent is reasonable, it is useful to eliminate

them from the model. If it is not reasonable, they should

remain, for the effect of their possible presence on the precision of the remaining results must be taken into consideration. As an extreme example, one might consider two components

with nearly the same half-life. Analysis of the two-component

model would result in answers having very large standard errors

- which, however, would allow overlap with the "truth". Elimination of one of the components would give a considerably

smaller standard error and perhaps a good "FIT" , but the result

could be quite wrong!

By way of summary, the least-squares analysis gives proper

estimates of initial rates and their standard errors only for

the correct model . Additional components make the standard

errors too large, whereas missing components make them too

small and may cause a poor FIT, etc., if the data are sufficiently sensitive. Even adjustments of half-lives, added variance,

etc., to obtain the best FIT may be misleading, and are less

desirable than independent (accurate) estimates of these

196
quantities. A poor FIT does indicate trouble, but a good FIT

may mean either that the model and data are correct or that

the data are insufficiently sensitive to indicate the difficulty.

E. Examples

1.

i2C(y,n) nc a. A simple, one -component, least-squares analysis , of

the decay of 20 min - C. All of the "indicators" are consistent with the model and data being correct* This particular

calculation has been checked with the Gumming (BNL) version

of CLSQ.

b. Effect of wrong half life (increased by 10%) * Note

that the result is wrong; that the FIT and one of the RATIO'S

exceed the limits provided; especially note the trend in RATIO

(+ - -)•

2.

65Cu(y,n) 64

Cu; 63Cu(y,xn ) 62Cu, 61Cu,

60Cu

Since counting times were available in minutes, it was convenient to set D(R) = 0, and T(R) = 0. a. Comparison of simultaneous equations (N - P = 4)

results with the least squares (Cumming-CLSQ) results (N = 22,

P = 4) . They are seen to be consistent; the least-squares

(N = 22) results have somewhat smaller standard errors; both

60 analyses indicate that Cu is "undetectable" by this method

(to be expected on the basis of the decay scheme and the method

of detection)

.

b. Same data, Cu eliminated from the model; all

indicators satisfactory. Note the significant decrease in the

CO

standard error for Cu.

a. 235U(n,f).. . A "trouble -shooting" example, unknown mixture of (I, Br,?)

fission products, very good counting statistics (~0.1%). Again

D(R) = 0, T(R) = 0. REM's 2-5 utilized.

a. A trial model - 4 components - additional standard

deviation (F) set equal to zero - all indicators unacceptable.

197
b* Two components added - all indicators still

unacceptable , but enormously improved.

c« For more rapid on-line TT trouble-shoot ingtT , only

the principal components (according to 3b) were retained, and

an added relative standard deviation of 1*0% (F = 0.01) was

included. Again, a large improvement has been effected, and

there appear no negative components. But, FIT is still larger

than its acceptable upper limit (~1.3), and RATIO 1 s exceeding

the appropriate limits (~±3.1) appear. (These latter - only

two points - might be outliers.)

List of references for Appendix I

[Al] Cumming, J. B. , "Applications of Computers to Nuclear

and Radiochemistry," G. D. T Kelley, editor, NAS-NS

3107, 25 (1963).

[A2] Nicholson, W. L. , Schlesser, J. E., Braver, F. P.,

Nucl. Inst. Meth. 25, 45 (1963).

198
APPENDIX I

- PROGRAM LISTING

Example la

8

10 DATA 7* 1 \Vj N*^

11 DATA 20 . 5* 0* 1 1 b* 59* F 12 DATA 16 *29 12 '1 C ) * M ( U ) 13 LATA 20 13 ri( 1 )

1 4 DATA 0* 16* 56* 1*9 43 14 ( i ( l ) * m ( l ) * u ( l ) * r ( l

)

15 DATA 0* 16* 57. 5* l*bby 1 5

1

1

16 DATA 0* 17* 18* 2*9 1^ 16 1

1

17 DATA 0.. 17*27*2* 657 1 7

it lb DATA 0* 18* 15* 3*240 18 1

1

19 DATA 0* 18*27* 3* 147 19 tt 20 DATA 0* 18* 53* 4* 137 2k) T ( 7 ) * M C 7 ) * U ( 7 ) * Y ( 7

)

KEY • READY.

RUN

WAITCLSO-1 13:37 UEIR 07/22/66

DEADTIME CMICROSEC3 =?0

TC.R3 (min) YCR3 (cpm) Y-CALCC R3 (cpm) SIC-MA-YCR3 (cpm) RATIOCR3

27. 5 922.5 920.871 30.708 3 5.30629 E 29 «68. 5 874.221 29.8 16 1 -. 191882

50 . 436. 5 422.221 15. 1 162 .944615

59 308 309.084 12.816 -8.^5709 F 107.5 59.5 57. 5544 5. 16398 .376762

119.5 28. 5 37.9717 4. 04145 -2.34365

146 13.75 15. 156^ 2.92618 -. 480625

FIT= 1.06 49 5

COMPONENT HALF-LIFE (min) CRM AT TC03 SIGMA (cpm)

1 ("Q 20 2388-44 41.2041

TIME: 4 SECS.

199
Example lb

13 DATA 22

RUN

UAIT.

CLSG-1 13:40 CEIR 07/22/66

deadtime CMICROSEC] =?0

TCR3 YCR3 V-CALCCR] SICMA-YC R3 RATIOCRD

27. 5 922.5 862. 304 30. 7 08 3 1.96026

29 8 68. 5 822.499 29.8161 1.54281

50 436. 5 424. 41

3

15. 1 162 .799602

59 308 319. 625 12.816 -.907031

107. 5 59.5 69. 3435 5. 16398 - 1.90619

1 19. 5 28. 5 47. 5125 4. 041 45 -4. 70437

146 13-75 20.6159 2.92618 -2.346 39

FIT= 2.54804

COMPONENT

1 HALF-LIFE22

CPM AT TC0J

2050.92

SIGMA

35. 5517

time: 4 secs.

200
Example 2a

130 LEI

131 LET

10 LATA

LATA

LATA

DATA

DATA

DAjya

DATA

LATA

LATA

1 1 12

13

14

15

16

17

18

RUN

D(R) = T(R) =

4* 4

20. 5* 0*

0*0

770. At 199.8* 24j

34. 5* 1* 1773

136* 5*2150

360* ge, 5222

1219* 40* 3579

9.9

CLS9- 1 14:06 CEIR 07/22/66

COMPONENT

12

3

4

TIME: 4

HALF-LIFE

64C 770.4

6l Cu 199.8

6°Cu 2 4

«Cu 9 .

9

SECS.

CrM AT 1(0)

IV 5.2 42 » 200.

363.22b | 344.

642.32 i 197.

1 16b 5. 6

J 139 T

t Full

SI CMA

b 5. 1 442 4 12.4

1 iv . 7^45 1 tt. 2 72 7. 4b 6

J 103.

6

1 . 2VV7. 57 | 543.3

" t Least Squares Results

Example;2b

10 DATA

13 DATA

RUN

4* 3

770. 4, 199.8*9.9

CLSG'- 1 14:09 CEIR 07/22/66

TCR3

35

138. 5

370

1239

1 f[R]

1752.5

409. 5

240. 6

68.975

Y-CALCCR3

1752. 59

403.702

242.669

68-606

SIGMA-YCR]

42. 107

9.27362

3. 61317

1. 49 562

RATIOCPD

-2.02254

.625221

-. 572518

.246747

EF1T= .bb29 31

COMPONENT

12

3

TIME:

HALF-LIFE

7 7 0.4

199.8

9.9

4 SECS.

CPM AT TC03

193.633

374.9 12

14294.8

201

SIGMA

4.81052

14.6535

502.071
Example 3a

10 DATA 30*4

11 DATA .2083*0*0

12 DATA 0* 417

13 DATA 11606.6*1260*402*137.4

14 DATA 417*60*2721672*482*60*2243552*547*60*19 10661

15 DATA 612*60*1658734*677*60*1448148*744*60*1274099

16 DATA 807*60*1170784*872*60*1058907*937*60*964782

17 DATA 1002*60*877473*1067*60*78^558*1132*60*740113

18 DATA 1197*60*68 1195*1262*60*627028*1458*60*500112

19 DATA 1523*60*470693*1588*60*438193*1653*60*409038

20 DATA 1654*120*^636974*1979*120*566404*2104*120*511170

21 DATA 2229*120/457669*260^*120*331485*2729*120*301380

22 DATA 7220.8*120*20019

23 DATA 7345.8*120*17903*7470.8*120*17746*7595.8*120*16260

24 DATA 8345.8*120*11144*8470.8*120*10441

130 LET D(R>=0

131 LET T(R) = 720 PRINT "RATIOCR)"

788 PRINT CY(R)-G)/Z*

RUN

WAIT.

CLSG-1 14:58 CEIR 07/22/66

RATIOCR3

40.4412 -7.19511 -19.7176 -20.2547 -26.2354

"28.8263 -.488943 5.29539 11.8713 11.3912

-8.21908 16.1895 15*6724 12-8908 11.5351

17.9331 15.5156 13.8419 -2.39846 -4.48345

.915454 -2.51648 -18.5074 -19.4957 -4.78326

-9.64747 -.353976 -1. 77907 7.95311 9.1763

FIT= 16.3558

COMPONENT HALF-LIFE CPM AT TC03 SIGMA

1 1 1606.6 -26.7601 .73906

2 1260 ' 8284.56 9.59787

3 402 22506*6 31.3352

4 137.4 17165-7 42. 1761

TIME! 12 SECS.

202
Example 3b

10 DATA 30*6

13 LATA 1 1606.6*21 18* 1260* 402* 137- 4* 53

RUN

CLSQ-1 15:08 CEIR 07/22/66

RATIOCR]

-3.20662 4.06967 6*79639 4*98505 -7.83793

-18.4923 3.05919 3*37929 5.94939 2*69947

-18*7797 4*82017 3*95512 1*26521 1.92481

9*35189 7*98302 7*41168 -5*82213 -4*87122

3*41721 2*71889 -6*00095 -4*92987 4*33862

"2.20876 4*95923 1*57886 -2-28829 -3.59305

FIT= 7.56546

COMPONENT HALF-LIFE CPM AT TC03 SIGMA

1 131

l 11606.6 104.936 6.20706

2

82 Br2U8 -1222.84 61.5783

3

133

i 1260 9645-92 85.6005

4

135

i 402 23255. 5 69.37

5

132

l 137-4 12193. 106.386

6

134

l 53 6667.34 105*744

TIME: 18 SECS.

203
xample 3c

DATA 30* A

1 DATA . 2083.»0>. 01

3 DATA 1260* 402* 137. 4* 53

LIN

-SG- 1 ATI0CR3

1.2088 5

1.83617

3. 5667

1.26625

2. 58219

5.39347

15:13 CEIR

1.23219

-. 402517

-.801904

1.375

2 . 79 7 48

-. 41429 7

07/22/66

1.8 39 09

-.725736

-.756434

1 . 59 1 58

1.8819

- 1.89842

1. 3925

-.68 3059

-.900714

•633133

2.04886

.765522

.229812

1. 12125

7.84277 E-2

1. 1328

1.84001

.999526

IT= 1.92825

OMPONENT HALF-LIFE CPM AT TC0] SIGMA

1 1260 7426. 17 33.4417

2 402 26577. 5 219. 441

3 137.4 638 1.34 833.754

4 53 1 1670.3 1220.81

IME: 11 SECS.

204
PROGRAM LISTING

CL.SQ-1 13:49 CEIR 07/22/66

1 REM MULTI COMPONENT DECAY CURVE ANALYSIS , 2 REM - IE ONLY RATIO(R) DESIRED, TYPE:

3 REM - - - 720 PRINT "RATIO(R)" - - 4 REM - - - 788 PRINT CYCR)-C)/2, = =

5 REM - IE N>35, OMIT COMMA AT END OE 788 C4 REM)

6 REM - IE MR) = 1* "FIT" = STD DEVN,

7 REM - AND "SI GMAC J) *"EI T" = STD ERROR(J)

100 DIM D( 100), TC 100), MC 100), UC 100), Y( 100), V.C 100)

1 10 READ N, P

1 1 1 READ B, S9,E

112 READ TC0),MC0)

113 PRINT "DEADTIME CMICROSEC) =" i

1 14 INPUT T

1 1 5 PRINT

1 16 LEt T = ('T/60)*lE-6

120 EOR J = 1 TO P

121 READ h(J)

122 LET LC J) = L0G(2)/H(J)

123 NEXT J

125 EOR R = 1 TO N

130 READ DCR)

1 3

1

READ T(R)

132 READ M(R) . 133 READ UCR)

134 READ Y(R)

140 LET VCR) = (C(Y(R)/U(R) ) T2)*(Et2+( 1/YCR)) ) + S9t2)tC-l)

1 ^i5 LET TCR) = 1440+DCR) + 60* < TC R) -TC 0) ) +M( R) -M C 0)

150 LET TCR)=TCR)+.5*UCR)

160 LET YCR) = C Y C R) /UC R) ) -B

161 LET YCR)= YCR)/C 1-YCR)*T)

168 NEXT R

2 1 EO R J = 1 TO F+l

220 FOR I = 1 TO P

230 LET BCI,J)=0

240NEXT I 250 n Ext j

260 FOR R = 1 TO N

270 FOR J = 1 TO P+l

205
28 FOR ,1 = 1 TO J

290 IF J = P+l THEN 320

300 LET A = W(R)*EXPC-C(L(J)+L(I)>*TCR>>)

310 GO TO 330

320 LET A = KR)*Y(R)*EXP(-L(I)*T(R))

330 LEI Bd* J) = E(I> J) + A

3*0 LET B(J*1)=BCI«J)

350 NEXT I 360 NEXT J

37 NEXT R

39 FOR I = 1 TO P

400 FOR J = 1 TO P+l

420 NEXT J

430 NEXT 1 440 FOR 1 = 1 TO P

-445 LET F(I) = 450 NEXT I 455 FOR A = 1 TO P

460 Le T B1=0

46s FOR G = 1 TO P

47fc IF F(G)<>0 THEN 49

475 1F(ABS(E1)-ABS(6(G.,G) > )>=0 THEN 490

480 LET BIsBCGjG)

48 5 LET L = Q

49 NEXT 6

^95 LET F(L) = B1

500 LET B(L,L)= 1 505 FOR K = 1 TO R 510 IF(K-L)=0 ThEN 560

515 IF b(K,L)=fc THEN 560

520 LET R1=B(K,L)/B1

525 FOR L> = 1 TO P

530 IF B(L*D)=0 THEN 555

535 IF <L-L)<>0 ThEiN 550

540 LET B(K, L>) = -R1

545 GO TO 555

550 LEI B(K, L)=E(K, D) - R 1*B(L, D)

555 NEXT b

56£ NEXT K

5 ^5 NEXT X

5 ?5 FOR K = 1 TO P

580 FOR D = 1 TO P

58 5 LET B(K, D)=B(K>D)/F(K)

206
600

610

620

6 30

6-60

645

650

655

6 59

6 60

6 70

6b

69

700

710

720

725

7 30

740

7 50

760

770

7b

78 1 782

78 3

784

78 5

786

78 7

788

789

79

79 1 79 5

799

8 00

801

805

810

900

'SIGMA-Y(P)"* "RATIO(R)"

NEXT D

NEXT K

FOR I = 1 TO P

LET C(I)=0

FOR J = 1 TO F

LEI C(I)=C(I)+B(1 J J)*B(J,P+1>

NEXT J

NEXT I IF N=P THEN 670

GO TO 720

FRINT ,, COMPONENT"> ,, hALF-LIFE".»"CPM AT T< 0) "* " SI CM A"

FOR J = 1 TO F

PRINT J.»H< J),C( J)j SGRCBCJ, J)

)

NEXT J

GO TO 9 00

PRINT "T(R) ,, J "YXR)"j "V -€ALC ( R) "* LET S1=0

FOR R= 1 TO N

LET G =0

FOR J = 1 TO P LET G = C+CC J)*EXP(-(L( J)*T< R) )

>

NEXT J

LET i. = SGRC 1/HR) ) LET SI = SI + K(R)*((V(R)-G) T2)

IF R = f THEN 79

IF R = 11 THEN 79

IF. R = 16 THEN 79

IF R =21 THEN 79

IF R = 26 THEN 790

IF R = 31 THEN 790

PRINT T<R>*Y(R>*G*2*<Y(R)-G>/2

GO TO 79 5

PRINT

GO TO 788

NEXT R PRINT

PRINT

PRINT , 'FIT="; SGRC S1/(N-P) ) PRINT

GO TO 670

END

207
APPENDIX II

FORTRAN PROGRAM FOR ANALYSIS OF MOSSBAUER SPECTRA

This appendix lists the Fortran program for analysis of

Mossbauer spectra. The input is divided into three parts:

instructions (figure 36) , identification and data.

The first card of the instructions consists of a plot (0)

,

or no-plot (1) in punch position one. The next five punch

positions are reserved for the fixed point convergence criterion. The second card contains the number of iterations in the

first two punch positions. The third card contains the number

of overflows in fixed point for a 100 K counts -per-channel

analyzer. The following cards contain the number of ignored

channels, one card for each channel. This set is terminated

by a zero card. Following the zero card is a set of cards

containing the estimated peak position and half-width for each

peak in the spectrum. The instruction section is terminated

by a blank card.

The identification section consists of 15 cards identifying

the spectrum or blank cards. Following this group are 20 data

cards for the 200 channel spectrum.

The readout associated with this program consists of a

plot and a channel -by-channel analysis of the spectrum. The

plot program is written for a Calcomp plotter and the spectrum

is inverted (figures 37, 38).

Modifications to the program are presently in progress to

allow the analysis of up to twenty peaks and to allow greater

flexibility of format, particularly with regard to the plotting

routine. Spectrum stripping capabilities are being incorporated,

and in addition, the plot routine is being modified to conform

with the format prescribed by the NBS Standard Reference Spectrum Program (e.g. inversion of the spectrum)-

Fortran 3600 cards for this program can be obtained from

W. L. O'Neal, Section 310.01.

208
We would like to acknowledge the assistance of Mr. A. L.

Polinger, of the Engineering Metallurgy Section, 312.01, for

making modifications to this computer program.

209
FTN5,10 04/QV«€

c 10

c 17

e 21

c 25

c 29

c 31

c 3?

c 35

c 37

c 39

c 41

c 43

c 45

c 46

c 47

49

58

51

32

53

54

55

56

57

c 58

60

61

6?

67

68

72

73

79

80

81

82

83

84

85

86

90

91

92

93

94

95

96

97

98

99

c 101

10?

103

104

105

PROGRAM PARLOR H ITERATIVE LEAST SQUARE F\1 TO PARABOLA PLUS UP »0 10 LORENTZlANS

ERsRATIU CONVERGENCE CRITERION

IT«NAX!.1UM NUMBER OF ITERATIONS

OV«COINT OVERFLO* FACTOR

J«IMBEDDFD CHANNbwS 10 8t IGNORED (IMBEDDED ZEROS MUST BE IGNORED

ALABL«i980 CHARACTER ALPHAMERIC FIELD FOR LABELING CASlS

FIRST 6 CHARACTERS Of AL *BL UBEt PUNCHED OUTPUT COLUMNS 75«80

»(I)*ESTJMATE0 LOCATION Op PEAK 1 ^(I)«EST1HATEB HALF-»*IPTN AT HALF-1AXMU1 OF PEAK I VdMCOUNTS IN CHANNEL I (CHANNELS 1*200)

ZERO TEST DETERMINES BEGIN AND END CHANNELS FOR CALCULATION

IF NO PREVIOUS ENU ZERO, CHANNEL 199 MUST BE ZEROED

ZERO TEST DETERMINES END OF EACH DATA SET OF ARBITRARY LENGTH

3ASE-LINE FOR PUNCHED SP£cTRU.4*HAXlNUM COUNTS

TAPE 02 GENERATES XY PLOT fOR EACH CASE

I) I HENS I ON VARA(lZl,VARP(l2) < tfARS(12),BASE(12)»VARG(12) # VARB(l2)

DIMENSION Y(200)«4(J3f34),B(34)*P{ll) # Pl(10)«R(10| ( H(ll)iHl(10)

f> I HENS I ON AA(33#34),B9(7Z0)*T(33.34).AINV(720)

DIMENSION OA(10> ( IG< 230)i ALABL<9* 15), Sl(l0)iGl(10)*ElClO),VlC2OQ>

niHENSlON XYPLOT(400),Y2(200)

DOUBLE PRECISION A,B,C»H»Hl»P«Fl

DOUBLE PRECISION *A,bB.T»AlNV

CALL PLOTS(XYPLOT»400,2)

REMIND 02

^EAD DATApDU ZERO TESTS, SET UP IGNORED CHANNELS

*EAD(5,61)!PL3T»ER

rORMAT<U,Fl4,0>

IF(EOF,5) 1700,67

R£AD(5,68)IT

P0RMATU4)

READ(5,73)OV

FORNATCF4.3)

DO 80 1*1,200

IGCI)*0

DO 84 I si, 200

READ(5,85)J

IF(J,EO,0)GO TO 96

!GU)*1

P0RMAT(J3)

IGNflGNwl

DO 93 NL«1,12

RE4D(5,94)P(NL)*H(NL)

IF(H(NL),EO.0»0)GO TO 95

CONTINUE

PORMATC2F7.0)

ML»NL"1

READ(5f97)((ALABLtI»J)iI*l«9).J«l«15)

roRMAT<9A8)

READ(5,99)(Y(I)(!«1,200)

roRMAT(10F7,0)

ZERO TEST FOR RESIN. END, IGNORED CHANNELS/FIND COUNT MAXIMUM

DO 105 Nisi, 200

|F<!G(Nl).NE,*)GO TO 105

IF(Y(Nl).NE«0«0)3O TO 106

CONTINUE

1547

15 X 15470

15470

)15470

15470

15470

15470

15470

15470

15470

15470

15470

15470

PLOT

15470

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PLOT

15470

PLOT

PLOT

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210
FTN5.10 04/07/6*

106 SN»0,0

107 r)0 HI N»Nl,200

108 IF<IG<N).NE.O>GO TO 111

109 IF<Y<N),EQ. 0.0)80 TO 112

110 !F(Y<N),6T.§M)gMiT<M

111 CONTINUE

11? S«N«1

C 114 SO«RPCT FOR ROUNf OVERFLOW. PUNCH AND PRINT ALPHAMERIC DATA

115 OO 116 J»N1#N

116 V<I)«Y<l)*OV*l,0E*.

117 |H*EM*l,0E5*OV

118 4RITE<6«119)

119 V0RMAT(lHl # 2CX)

120 riRITe(»«121H(AL44L<!»J)<lal*9>»J>l ( 15>

121 F0RMATC1X,9A8>

122 CONTINUE

123 CONTINUE

124 CONTINUE

C 126 NORMALIZE COUNTS, 00 PRELIMINARY CALCULATIONS

127 00 128 I>Nl*N

128 Y(!)»Y<n/EM

130 l!»5*NL*4

140 l8»L1»1 150 00 157 I«1,NL

155 J(l>.l t J/(H(!HH(ll)

157 OA<I)»0 f 160 LIM*0

161 LIMQ*0

16? 80 TO 170

165 00 167 Ml.NL

167 0A<I)»A(3*I«2 t LlJ

C 169 FILL LEAST SQUARES MATR!<

170 00 210 J'l.Ll

180 00 210 I»l# — L2

ERROR

200 A(!*J)»0,0

210 CONTINUE

230 00 390 K«N1«N

235 IF(I6(K).ME«0)6O TO ?90

240 C«K

250 00 280 I *1«NL

255 J«3»I

260 B(J«»«l v 0/UtQ*i4(l>*CC»Pcm«*2J

270 8<J«l)PB<J«2)*8CJ«2)*(C!fP{I))

280 9<J)«B<J»l>*<e*IMP»

290 DO 300 I«l,3

300 9(L2«3*l)sC**U«i)

320 00 390 J*1»L1

330 00 390 I *1«J

340 IFCJ.E0.LD60 TO #70

350 A<!«J>«A<ItJ>*B(ll*B(J>

360 90 TO 390

370 tFd.EO.LDGO TO 490

380 A(It J)"A(I«J)t8(!>*V<K)

390 CONTINUE

C 460 SOLVE LEAST S8UAR5S MATRIX

19470

15470

15470

19479

19470

19479

i 19479

19470

19479

19479

19479

19479

19479

19479

19479

19479

19479

19470

19479

19479

19479

19479

19479

19479

19479

19479

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19470

19479

19479

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19479

19479

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19470

211
fTN5,lO 04/07/44

470 00 490 J«ltW2

480 90 490 iPltJ

48? *A<!t J)«A(tt J)

484 AA(j»I>*A(I* J)

490 A(J ( !>*6<I»J>

900 00 690 I«1.L2

510 00 MO J-H.2

920 !r(A(!»J)»EQtl. 0)«)O TO 930

530 00 9*0 K«1.U

940 8<K)*A(!«K)

950 A<!#K)"A(J,K)

960 A(J|K)«S(K)

970 SO TO 600

960 CONTINUE

990 90 TO 490

600 C"A(!,I)

610 DO 620 K*l.Ut

620 A(I,K)»A<I»KHC

630 00 680 K«l.l,2

64Q IHK.EO.DGO TO 6|0

450 e«A(K«I)

660 00 670 J«1,U1

670 A(K«J)«A(K*J>9e*A(I«JJ

680 CONTINUE

690 CONTINUE

695 CORRECT PEAK LOCATION AND WIDTH. PRINT RESULTS

690 *RITE<6»780)

700 DO 709 IO«l«M.

701 JQ* 3*10

702 «<IQM A(JQ«2|Ll*

703 Ml<!Q)« -A(je«Li>/H4Ia)

704 ir((H(lQ)«HKIon f 6T f e;e>60 TO 709

705 irltiHO.OT. 10)60 TO 711

706 l]NQ» LIMQ * }

707 »<!Q>« 1,1»H<1Q)

'707 riR!TE(6»770HiPt!>tSlf !>*BKI>«QX(I)

708 90 TO 1*5

709 CONTINUE

718 80 TO 715

711 4RITK6, 712)10

712 F0RMAT(//34M WRON8 HKFWIdTN ESTIMATE FOR P§AK t l5)

713 80 TO 1400

715 00 760 !>l.Nl

717 J»3«l

719 4<I)«A(J-2,Ll)

720 Pl(I)«A(J«lfLi)/<S v O*Hf !}*R(M)

725 P<I>»PCt> * Ptlll

73? 41(I)«-A(J«L1)/R<I>

734 M(MiMU)« O v f*HtfI)

736 5l«I)«l»6/SQRT(H<m

740 EKI)*RU)*6M

750 81<I)«SKI)«E1CH*3, 14159

760 tfRITEC4,770)I«PU>*Sl(I)«6l(I),Gl(I)

77Q PORNAT(1X,I2 # 4E20,8)

7800PORNAT(//10X,8HNEM »EAK f llX»14M4EW HAlF»UlDTM,7X«10MNEW

7801.8HNEH AREA)

19470

19470

1947S

19470

15470

15470

19470

15470

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15470

19470

15470

19470

15470

19470

19470

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1947S

19470

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i9470

19470

19470

19470

19470

19470

19470

19470

MIISMT, 10X19470

19470

212
rfNftti 04/87/66

C 805 T|8T NUMBER OF IVeRATXOSJ!) AMD CONVERGENCE

•20 IPCkfM ,GE. IT) M TO 1680

•10 DO 043 I«1#NL

•39 ir(A»f«Hi(|}/n(m,6?«giiiao To 165

840 irfAOt(Rl(I)/f(l>NOT t fR>QO TO 1*5

•4? !MAM<<R(I>*OAU>)/RU>>;<T f E*>dO TO 16*

•43 CONTINUE

«44 »UNCH riHAL MAK BARAME78RS

•46 CONTINUE

•4? CONTINUE

•48 00 «49 l«l«20l

•49 u<n»o,o

•90 S«0 V C *91 MINT F|T AND DAT* FOR EACH CMANMEL.FIND NAXJNU" OF

t«9i »ARA0«A(L2«2,(.l)«fiH

3451 RARA1«A(L2-1*W1)*6N

3(91 PARAt«A(L2,Ll)*EN

4691 4RITE<6 t 9t91)RAKA0«RARAl*RARA2

9691 FORNATt//5X*10HPARA90lA» ,Fl5;B.«H * C •E15,8t7M)«C * 9*511 9M>*C«G)

•92 4RITE<4,654)

•44OoRftAT<//7X*5RCMNU«6X*llMiORGNTXJANS# 9X«0HJ>ARAHQi.A»

•541. PAR».7X,8MRSSJDYAL»

•96 VN»0,0

•61 00 935 K*N1«N

•62 1F<16(K),NE«0>00 TO 935

•69 T2fK)«0,0

•70 6«K

•79 00 ••• l«l»NL ••• T2(KMV2(K)*RCI)/(l«0*MU)*CC<R(in**2)

•90 RAR«AfL2*2.Ll)«C*Ua2«l»Ll>*C*A<L2«U>)

910 U«KMW>-PAR

910 0»Y1(K^»T2(K)

929 MS*0**2

927 8«V1(K)*EN

926 RAR9RAR*EN

929 E«V2(K>*EN

93* |F(VN,6T,T2(K})YNVY2(K)

931 tfR!TEf6f949)K«6«PAR«6.0

939 CONTINUE

937 TN9TM**!

940 roRMATflX,U0 # 4E29t«>

990 B»tQRTCS/<N»M-|QN»L2>)*6M -. „

960 4RtTt(6.96l)D*tM 955 D1 = D

961 rOMAT(lHO«*A«ERA0E MEAN SQUARE RESIDUAL »*E17 ( 8**0X

iNtiR OF C0UNT6 •«F10 f 0i///)

966 IFflRLOT.EOfDOO TO 1177

e 967 »10T NORMAL I I8D FJT AfJO OaTA

966 00 961 K«N1«N

969 IF(I«CK),NE f O)03 TO 961

970 0»«/ll.l

•71 6*Yt(KI/VM

972 CALL SYMBOL<D#G..98«1>0,<I»-1)

973 |«Y1(R)/YM

974 IF<E*t4)978*976«<"6

15*70

15470

15470

15470

15470

l!5470

15470

15470

15470

15470

15470

LORENTZIAN FIT15470

15470

15470

15470

(.E15.8.

15470

12X»13MC0UNTS 15470

15470

15470

15470

15470

15470

15470

15470

15470

15470

15470

15470

15470

15470

15470

15470

15470

15470

15470

15470

15470

*24HMAXIMUM NU

15470

15470

PLOT

PLOT

PLOT

PLOT

PLOT

PLOT

213
r?N5,10 04/07/44

975 !F<i.OT v 10,4)QO 1'J 960 PLOT

976 CALL SYMB0L<D»E«t >>6f3.9,.),«l) pt0T

977 80 TO 9S1 PLOT

978 CALL SYM8Ol(D«*t3.,06,6*l80 ( 0,9l} r|>0T

979 80 TO 981 PLOT

980 CALL SYH8OL(D«10,l» v 09i6*0*0*«l) PLOT

981 CONTINUE PLOT

C 984 ORAM AND TICK X AND Y AXES 15478

965 CALL PLOT(0»0#0tS«3) PLOT

986 CALL PLOT(20,8.0,I,2) pLOT

987 00 M9 |al»2l PLOT

968 0»2l-I PLOT

969 CALL SVMBOLCD»0,3.U2.13»0.0.ti> PLOT

990 CALL PLOT<0,C,l8,0#2> PLOT

991 90 993 l«l,ll PLOT

992 9»11-I PLOT

993 CALL SYMBOLlO»0»0**12.13.90 t O*-l) p^0T

C 994 NUMBER AND LABEL AXES 15470

995 00 1020 1»1.201#19 PLOT

000 J«l«l PLOT

010 0»J/10,0»,24 PLOT

020 CALL NUMBER(Dft2i,,14,j.0.0«2H|3) PLOT

030 BO 1646 l*l«14 PLOT

Q4Q 0M»1 PLOT

050 6»D/10,0 PLOT

060 GALL NUMBER<«»43,!),,14,E«0,0«4HF3,1) PLOT

070 CALL SYMBOL<9j00»«.§0,j2l.7HCHANNIU0,0#7> PLOT

060 CAUL SYMBOL<»0,50|2 ? 00j0 f 2i#15HNORM» COUNTS X ,90f0»15) 15470

061 Q»YH*SH# l Q+fl 15470

082 CALL NUNBER(«6 f 59*6 f 0,0 v 2l.D»90,a«5MEl2 t 5) 15470

084 PLOT ALPHAMERIC DATA AND LEGENO 15470

090 CALL SYMBOL<0«5fl0.0,0:i4,ALABl<l«l)*0.0,S> 15470

170 CALL PL0T(36. 0*0, 8#«3j PLOT

176 PUNCH COUNTS MINUS PARABOLA F OR EACH CMANNEL< IGNORED COUNT8»0J 15470

177 CONTINUE

178 CONTINUE

160 90 1186 laNlfN 15470

162 IPUO(I).NEf0>GO TO 1186 15470

184 YlCI)«EM*mU)*lf0) 15470

186 CONTINUE 19470

1188 §0-41*4 V*U1*1+ 1* 15470

190 K"J*9 15470

192 LRK'IO 19470

194 CONTINUE

196 CONTINUE

200 MR!TE<6|1205)

1265 rORN4T<2Hl »19H Sjjggg ANAlVSU)

210 00 1225 !«1#U

""

215 90 1225 J«1«L9

220 IJ»J*<<l«t)*<a*L2*I>>/2

225 BB<!J>*AA(1«J>

230 IPSING«0

235 CALL TR}AN4BS»L?«?*T«U!F8!NG»

240 IF<tPSING,EQ.I)GO TO 1259

245 80 TO 711

250 CALL TTNPY<T»L2«A!NV»l2,0>

-1207 D = Dl

214
FTN5.10 64/lf/4*

1300 WRITE (6.1310)

1310 roRHAT (2X,1UH VARIANCES*

1320 !PAR«(L2*U2*1)>'2

1330 VRPR0«D*SQRT(AlNVUPAR*9))

1340 VRRR1«0*S0RT<AIM«(IPAR«2>)

1350 VRPR2»D*SQRTUlNV|!PAR-0>)

1360 WRITE <6.1362>PARA0#VRPR3

1362 fORHAT(4X.5H AO* #El5 f 8, »X»6H VA4« .E15.6)

1364 4R!TE(**1366)PARAl*VRPRl

1366 P0RMAT(4X,9H Al« .E15,8,4X.6H yA*s ,E15,3)

1366 WR!Te<*tl37Q>9ARA*,VftRR2

1370 F0RHATUX,5H A2« «El$,8.*X.6H V<H« .€15, 3)

1375 WRITE<7tl377>ALA«L(l*l)

1377 rORMAT(AS)

13gO WR!TE(7.1390>RARAO,VKPRO*PARA1 > V.-«PR1«PARA2«VRPR2*ALABLI1|1)

1390 rORMATUEt2.5,A8*

139? 4RITEC6«1394)

1394 F0RMAT«4X,5H PEA<<»7X,9h 9 0SITI0N. llx. 15H HALFmI0TH<*HMAX,7X*

1 7H HEIGHT. 12X»5M ARiA.l5X«9H BASELINE)

1400 HO I960 I*1*NU

1410 !VA»(3*I-2)*<«3*{-3)*C2*l.2»3*I*2J)/2

1420 VARA(I>«0*SQRT(AI*VUVA)>

1430 !VP«<3*!-l)«((3*I>2)*(2*U2«3*l*l))/2

1441 COVA*(AINV(IVA))/IEl<I)*Elf I))

1442 aOVP><A!NVUVR>>/lA(3*l.l,t.l)»A(3*l*l # Ll>>

1443 COVAP* (AINV(iVA*l))/(A(3*!-l*|.l>*El(!))

1444 0OVc8ORT(COVA*COVR*C0VAP)

1445 VARP(I>* D*<At3*l-l#Ll)/C2.0«H<I>*EKI> ))«CQV

1450 !VH« (3*!)4. <<3*!-l>*<2*t.2*3M))/2

1461 eOVAs(AINV(IVA)l/(El(!>*El(I))

1462 00VH>(AINV(IVH))/(A(3*l«l t i.l>*A(3*!,l f l.l))

1463 C0VAM«(AINVMVA*2)>/(A(3*I.L1) •£!(!))

1465 VARH «D*(A(3*I«U1)/E1(I) >*SORT(COVA*COVH*COVAH)

1470 VARS<I>« SlU)*CVARH/H(p)/2.0

C PRINTOUT OF VARIANCES

1915 8ASE(!>* PARA0*PARAl*P(p* PARA2*P( ! )*P( I ) 1520 VARQfP* <ABS<VAR»<P/Sl(p)* ABS< VaRa( I )/El( I ) I >»Gl< I ) 1929 tfARB(I)*VRPRO* VRPR1 * V^pR2

1530 WRITgC7 # 1535>I.PU)»SlCP.El«n»'31C|).BA$EU)rAl.ABLCl»l)

1931 WRITE<7,S539)!,VARPCI),V*RS(I)»V*RAJ!).V4RQ(I),V*R8(I).AlABlfl.l»

1935 PORNAT(l2*9E14 r 6«4e)

1990 MRITEC6.1555)I.P(I),Sl(I)*El(I>'61f l).BASE(I)

1599 F0RHAT(4X»|3.»e28»8)

I960 WRlTE<6*1965>VARPU)*VARS(I)»tfARA(I)«VARQ(I)«VAH8<I)

1969 FORMAT <4X,8MVAR I ANCi»5E23;«)

1600 30 TO 60

1700 REWIND 02

1600 STOP

1900 END

215
!

f,lA PARlORM

PROGRAM LENGTH 31374

ENTRY aOlNTS PARLOR* 262-Sl

EXTERNAL SYMBOLS

08QENTRY

THEND.

Q1Q10210

Q1Q10020

02007220

Q1O04210

01005210

01002210

08QST0P*

QSODlCf

.

PLOTS

SYMBOL

PLOT

NUMBER

TRI4N

TTMPY

SQRTF

QSQIFEdK

Rfckf* TSM«

STH«

ONSfNGLf

QNDBUBL*

01117 SYMBOLS

04/07/66 ED

10ENT PARLORM

216
FTNf.10 04/97/**

SU8R01TINE TTIJpyiT.«i,A.K.!rTL)

DIMENSION T<100>tAU00)

DOUBLE PRECISION A,T

NX2»N*2

IJ*0

IF (IFTL.NE.D 60 TO JO 00 20 1*1,

K

00 20 JsJ.K

IJ«IJ*1

*(U)«0,DO

DO 10 L»1»I

Il»I*((L-D*(NX2rL))/2

I2«I1*J-I

20 *(U)«A(IJ)*T(I1)«T(I2)

20 CONTINUE

RETURN

30 DO 50 1*1,

K

NO«K»I*l

VPT»((NX2-I)»U-l>)/2

JJ»1

DO 50 J«I,K

U«I*JJ*1*NPT

!2»I*JJ<»l*<(*X2«J)*<,J.l>)/2

IJ»IJ*1

A(IJ)«0,D0

DO 40 L»l,NO

A(IJ)«A(IJ)*T(Il)fT(I2)

U»U*1

40 12312*1

JJ»JJ*1

50 NO»NO»l

RETURN

END

217
ftlA TRN'V Q4/07/66 ED

RROSRA* LENGTH

ENTRY »OINTS TNMRY

EXTERNAL SVHBOLS

0400 I CT.

00126 SYMBOLS

00367

03003

10ENT TRHPf

218
FTN5.10

TO 150

DIMENSION A< 12751, T(1275»,TINV(1275i DOUBLE^RECISION A.T.TMv.TEHM.O*E.IERO.DiORT

<A*«0

DNE«1.D0

ZERO'0,00

MA*(N*(N*l))/2

30 10 !»1,MA

19 TC

I

>«A( I > TJ'O

00 90 J»1.N

00 80 I«J,N

J1*J

IJ*IJ*1

TEMP0»T(IJ)

IF U.GT.J) G« TO 63

IF (Jl.GT.l) QO TO 50

IT (TEMPO. LE.ZEH'J) GO

T<IJ)*DSORT(TRmPJ)

30 TO 80

J1»J1-1

Il*I*<(Jl-ll*(NXi«Jl))/2

TEMP0»TEMP0-T(I1»«T(I1)

30 TO 20

IF" (Jl.GT.l) GO T<J 70

I1«IJ-I+J

T(IJ)«TEMPO/T(U)

CALL OVCHKU)

IF (L.EQ.l) GO TO 150

90 TO 80

Jl»Jl»l

Il*I«Ujl-l)*(sX2-Jl))/2

I2»I1«J*J

TEMP0«TEMP0^T<U)«T(I2)

SO TO 60

CONTINUE

CONTINUE

IF CK.EO.O) GQ TO 170

00 100 1*1, NA TINV(I)«T(I)

IJ«0

DO 140 J»1,n

00 130 I«J,N

IJ«U*l

Jl»J

TEMP0«Z6R0

IF (I.GT.J) G0 TO 110

TINV(IJ)«0NE/T<IJ)

CALL DVCHK(L)

IF (L.EQ.l) GO TO 150

30 TO 130

110 fl>!*<(Jl->iJ*(ifX2sjl)»/2

I2»Jl*<<J-l>*<NX2-J))/2

TEMP0»TEMP0»TIHV(|1)*TINV(I2)

IF (I"Jl.LE.l) GO TO 120

04/07/66

20

50

60

70

80

90

100

00021

00021

00021

00021

60021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

219
FTN5,10 04/07/66

Jl»Jl*l

30 TO HO

120 UM*CCl«l>*CIU2-l>)/2

TINV(IJ)«TE«PO/T(U)

CALL DWCHKCU)

ir (l.eq.1) r.e tj 150

130 CONTINUE

140 CONTINUE

RETURN

150 4RITF (6.160)

160 TORMAT U6H SINGULAR HATRfX)

<AV«-1

170 RETURN

5NO

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

220
9tl* TR!»N 04/07/46 ED

i 10ENT TRIAN

PROGRAM LENGTH 00614

ENT«V POINTS TH1AN 00010

EXTERNAL SYMBOLS

THENO.

Q8U0ICT

OVCMK

DSORT

STW,

00176 SYMBOLS

221
FTN5.10 04/07/66

10

20

30

40

50

60

SUBROUTINE THNOT<r,N^,Ml,NCt4, TJ.EFT)

n I MENS I ON T<U75).rt<^59 0),M2500>

INTEGER TLEFT

DOUBLE PRECISION r,tf, 4 MX2»2*N

JJ»1

MB«NC*N*

00 10 I«1»*B

J(I)*0.D0

IF <TLEFT,EQ.0> W TO 40

00 30 Jsl.NC

HRSUB«NH-(J-i }

00 30 J«1,NH

00 20 L«1»I

•4Ts!*UL-l>*<NX2iu>)/2

«tR»NRSUB*L

X<IJ)»H<IJ)*T(Mri«R(H^)

IJ«IJ*1

RETURN

00 60 J«1,NC

«<TSUB«<<J-l»*(NX2-J))/2

00 60 I«1»NR

00 $0 L«J*NC

HR»(L-1>*NR*I

*T*NTSUB*L

rf<IJ>«M<!J>*T<*T>«R<M«>

IJ«IJ*1

RETURN

END

00621

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

00021

222
t»lA TTMRY 04/97/66 ED

IDE»«T TT*«»Y MOflRA* LENGTH O0J«2

ENTRY •OINTS TTwPV OOOS

EXTERNAL SYMBOLS

0800! CI.

99111 SVNBOLS

223 »U.S. GOVERNMENT PRINTING OFFICE: 1966—251-021/411


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